Cellulose esters and their production in halogenated ionic liquids

ABSTRACT

Ionic liquids and cellulose ester compositions and processes for producing ionic liquids and cellulose esters. Cellulose esters can be produced by esterifying cellulose in a reaction medium comprising one or more halide ionic liquids and at least one binary component. Cellulose esters prepared via the methods of the present invention can have a degree of substitution (“DS”) of at least 1.5 and can comprise a plurality of ester substituents, where at least 50 percent of the ester substituents comprise alkyl esters having a carbon chain length of at least 6 carbons.

RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Pat. App. Ser. No. 61/028,280, titled “CELLULOSE ESTERS AND THEIR PRODUCTION IN HALOGENATED IONIC LIQUIDS,” filed Feb. 13, 2008, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to cellulose esters and/or ionic liquids. One aspect of the invention concerns processes for producing cellulose esters in ionic liquids.

2. Description of the Related Art

Cellulose is a β-1,4-linked polymer of anhydroglucose. Cellulose is typically a high molecular weight, polydisperse polymer that is insoluble in water and virtually all common organic solvents. The use of unmodified cellulose from wood or cotton products, such as in the housing or fabric industries, is well known. Unmodified cellulose is also utilized in a variety of other applications usually as a film (e.g., cellophane), as a fiber (e.g., viscose rayon), or as a powder (e.g., microcrystalline cellulose) used in pharmaceutical applications. Modified cellulose, including cellulose esters, are also utilized in a wide variety of commercial applications. Cellulose esters can generally be prepared by first converting cellulose to a cellulose triester, then hydrolyzing the cellulose triester in an acidic aqueous media to the desired degree of substitution (“DS”), which is the average number of ester substituents per anhydroglucose monomer. Hydrolysis of cellulose triesters containing a single type of acyl substituent under these conditions can yield a random copolymer that can comprise up to 8 different monomers depending upon the final DS.

Ionic liquids (“ILs”) are liquids containing substantially only anions and cations. Room temperature ionic liquids (“RTILs”) are ionic liquids that are in liquid form at standard temperature and pressure. The cations associated with ILs are structurally diverse, but generally contain one or more nitrogens that are part of a ring structure and can be converted to a quaternary ammonium. Examples of these cations include pyridinum, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, oxazolium, triazolium, thiazolium, piperidinium, pyrrolidinium, quinolinium, and isoquinolinium. The anions associated with ILs can also be structurally diverse and can have a significant impact on the solubility of the ILs in different media. For example, ILs containing hydrophobic anions such as hexafluorophosphates or triflimides have very low solubilities in water, while ILs containing hydrophilic anions such chloride or acetate are completely miscible in water.

The names of ionic liquids can generally be abbreviated according to the following convention. Alkyl cations are often named by the first letters of the alkyl substituents and the cation, which are given within a set of brackets, followed by an abbreviation for the anion. Although not expressively written, it should be understood that the cation has a positive charge and the anion has a negative charge. For example, [BMIm]OAc indicates 1-butyl-3-methylimidazolium acetate, [AMIm]Cl indicates 1-allyl-3-methylimidazolium chloride, and [EMIm]OF indicates 1-ethyl-3-methylimidazolium formate.

Ionic liquids can be costly; thus, use of ionic liquids as solvents in many processes may not be feasible. Despite this, methods and apparatus for reforming and/or recycling ionic liquids have heretofore been insufficient. Furthermore, many processes for producing ionic liquids involve the use of halide and/or sulfur intermediates, or the use of metal oxide catalysts. Such processes can produce ionic liquids having high levels of residual metals, sulfur, and/or halides.

SUMMARY OF THE INVENTION

One embodiment of the present invention concerns a process for making a cellulose ester. The process of this embodiment comprises (a) introducing a reaction medium comprising cellulose, a halide ionic liquid and a binary component into an esterification zone; and (b) combining at least one acylating reagent with the reaction medium in the esterification zone to esterify at least a portion of the cellulose thereby producing the cellulose ester.

Another embodiment of the present invention concerns a process for making cellulose esters. The process of this embodiment comprises (a) dissolving a cellulose in a halide ionic liquid to thereby form an initial cellulose solution; (b) contacting the initial cellulose solution with a binary component and an acylating reagent under conditions sufficient to provide an acylated cellulose solution comprising a cellulose ester; (c) contacting the acylated cellulose solution with a non-solvent to cause at least a portion of the cellulose ester to precipitate and thereby provide a slurry comprising precipitated cellulose ester and at least a portion of the halide ionic liquid; (d) separating at least a portion of said precipitated cellulose ester from said halide ionic liquid to thereby provide a recovered cellulose ester and a separated halide ionic liquid; and (e) recycling at least a portion of the separated halide ionic liquid for use in dissolving additional cellulose.

Still another embodiment of the present invention concerns a composition comprising a cellulose ester having a degree of substitution (“DS”) of at least 1.5 and comprising a plurality of ester substituents, where at least 50 percent of the ester substituents comprise alkyl esters having a carbon chain length of at least 6 carbons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram depicting the major steps involved in a process for producing cellulose esters in ionic liquids;

FIG. 2 is a more detailed diagram of a process for producing cellulose esters, depicting a number of additional/optional steps for enhancing the overall efficacy and/or efficiency of the production process;

FIG. 3 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 4 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 5 molar equivalents of acetic anhydride;

FIG. 5 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 6 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride at 80° C.;

FIG. 7 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 8 is a plot of absorbance versus time showing the dissolution of 5 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 9 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 10 is a plot of absorbance versus time showing the dissolution of 10 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 11 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 80° C.;

FIG. 12 is a plot of absorbance versus time showing the dissolution of 15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 13 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molar equivalents of acetic anhydride and 0.2 molar equivalents of methane sulfonic acid at 100° C.;

FIG. 14 is a plot of absorbance versus time showing the dissolution of 15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride and 3 weight percent acetic acid;

FIG. 15 depicts the proton NMR spectra of a cellulose acetate prepared by direct acetylation before and after randomization;

FIG. 16 is plot of weight percent acetic acid versus time for the esterification of acetic acid, as determined by infrared spectroscopy;

FIG. 17 is a plot of absorbance versus time showing the removal of water from 1-butyl-3-methylimidazolium acetate prior to dissolution of cellulose;

FIG. 18 is a plot of absorbance versus time showing the dissolution of 10 weight percent cellulose in 1-butyl-3-methylimidazolium acetate and 0.1 molar equivalents of zinc acetate at room temperature;

FIG. 19 is a plot of absorbance versus time showing the acetylation of cellulose dissolved in 1-butyl-3-methylimidazolium acetate with 5 molar equivalents of acetic anhydride and 0.1 molar equivalents of zinc acetate;

FIG. 20 is a spectral analysis showing infrared spectra of 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate upon first and second additions of 0.5 molar equivalents of acetic anhydride;

FIG. 21 is a plot of relative concentration versus time for 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate upon first and second additions of 0.5 molar equivalents of acetic anhydride;

FIG. 22 is spectral analysis showing infrared spectra of 1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium acetate, and a spectrum after 1 equivalent of acetic anhydride has been added to the 1-butyl-3-methylimidazolium formate in the presence of 2 molar equivalents of methanol;

FIG. 23 is a plot of relative concentration versus time for 1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazolium acetate upon addition of 2 molar equivalents of methanol and then upon addition of 1 equivalent of acetic anhydride;

FIG. 24 is a plot of absorbance versus time showing the dissolution of water-wet cellulose in 1-butyl-3-methylimidazolium acetate at 80° C.

FIG. 25 is a plot of absorbance versus time showing the esterification of water-wet cellulose dissolved in 1-butyl-3-methylimidazolium acetate;

FIG. 26 is a spectral analysis showing the ring proton resonances of cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium acetate (top spectrum), and the ring proton resonances of cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium chloride (bottom spectrum);

FIG. 27 is a spectral analysis showing the ring proton resonances of cellulose acetates prepared from cellulose dissolved in 1-butyl-3-methylimidazolium acetate after water addition (top spectrum) and before water addition (bottom spectrum);

FIG. 28 is a plot of viscosity versus frequency showing the viscosities of various solutions of 5 weight percent cellulose dissolved in 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride with 5 weight percent acetic acid, and 1-butyl-3-methylimidazolium chloride with 10 weight percent acetic acid at 25, 50, 75, and 100° C.;

FIG. 29 is a plot of viscosity versus frequency that compares the viscosity of 1-butyl-3-methylimidazolium chloride containing no co-solvent with the viscosity of 1-butyl-3-methylimidazolium chloride containing methyl ethyl ketone as a co-solvent; and

FIG. 30 is a plot of absorbance versus time comparing the degree of substitution and reaction rates during esterification of cellulose dissolved in 1-butyl-3-methylimidazolium propionate versus dissolved in 1-butyl-3-methylimidazolium propionate containing 11.9 weight percent propionic acid.

DETAILED DESCRIPTION

FIG. 1 depicts a simplified system for producing cellulose esters. The system of FIG. 1 generally includes a dissolution zone 20, an esterification zone 40, a cellulose ester recovery/treatment zone 50, and an ionic liquid recovery/treatment zone 60.

As shown in FIG. 1, cellulose and an ionic liquid can be fed to dissolution zone 20 via lines 62 and 64, respectively. In dissolution zone 20, the cellulose can be dissolved to form an initial cellulose solution comprising the cellulose and the ionic liquid. The initial cellulose solution can then be transported to esterification zone 40. In esterification zone 40, a reaction medium comprising the dissolved cellulose can be subjected to reaction conditions sufficient to at least partially esterify the cellulose, thereby producing an initial cellulose ester. An acylating reagent can be added to esterification zone 40 and/or dissolution zone 20 to help facilitate esterification of the dissolved cellulose in esterification zone 40.

As illustrated in FIG. 1, an esterified medium can be withdrawn from esterification zone 40 via line 80 and thereafter transported to cellulose ester recovery/treatment zone 50 where the initial cellulose ester can be recovered and treated to thereby produce a final cellulose ester that can exit recovery/treatment zone 50 via line 90. A recycle stream can be produced from cellulose ester recovery/treatment zone 50 via line 86. This recycle stream can comprise an altered ionic liquid derived from the ionic liquid originally introduced into dissolution zone 20. The recycle stream in line 86 can also include various other compounds including byproducts of reactions occurring in upstream zones 20,40,50 and/or additives employed in upstream zones 20,40,50. The recycle stream in line 86 can be introduced into ionic liquid recovery/treatment zone 60 where it can be subjected to separation and/or reformation processes. A recycled ionic liquid can be produced from ionic liquid recovery/treatment zone 60 and can be routed back to dissolution zone 20 via line 70. Additional details of the streams, reactions, and steps involved in the cellulose ester production system of FIG. 1 are provided immediately below.

As mentioned above, cellulose can be fed to dissolution zone 20 via line 62. The cellulose fed to dissolution zone 20 can be any cellulose known in the art that is suitable for use in the production of cellulose esters. In one embodiment, the cellulose suitable for use in the present invention can be obtained from soft or hard woods in the form of wood pulps, or from annual plants such as cotton or corn. The cellulose can be a β-1,4-linked polymer comprising a plurality of anhydroglucose monomer units. The cellulose suitable for use in the present invention can generally comprise the following structure:

Additionally, the cellulose employed in the present invention can have an α-cellulose content of at least about 90 percent by weight, at least about 95 percent by weight, or at least 98 percent by weight.

The cellulose fed to dissolution zone 20 can have a degree of polymerization (“DP”) of at least about 10, at least about 250, at least about 1,000, or at least 5,000. As used herein, the term “degree of polymerization,” when referring to cellulose and/or cellulose esters, shall denote the average number of anhydroglucose monomer units per cellulose polymer chain. Furthermore, the cellulose fed to dissolution zone 20 can have a weight average molecular weight in the range of from about 1,500 to about 850,000, in the range of from about 40,000 to about 200,000, or in the range of from 55,000 to 160,000. Additionally, the cellulose suitable for use in the present invention can be in the form of a sheet, hammer milled sheet, fiber, or powder. In one embodiment, the cellulose can be a powder having a mean average particle size of less than about 500 micrometers (“μm”), less than about 400 μm, or less than 300 μm.

As mentioned above, an ionic liquid can be fed to dissolution zone 20 via line 64. The ionic liquid fed to dissolution zone 20 can be any ionic liquid capable of at least partially dissolving cellulose. As used herein, the term “ionic liquid” shall denote any substance containing substantially only ions, and which has a melting point at a temperature of 200° C. or less. In one embodiment, the ionic liquid suitable for use in the present invention can be a cellulose dissolving ionic liquid. As used herein, the term “cellulose dissolving ionic liquid” shall denote any ionic liquid capable of dissolving cellulose in an amount sufficient to create an at least 0.1 weight percent cellulose solution. In one embodiment, the ionic liquid fed to dissolution zone 20 via line 64 can have a temperature at least 10° C. above the melting point of the ionic liquid. In another embodiment, the ionic liquid can have a temperature in the range of from about 0 to about 100° C., in the range of from about 20 to about 80° C., or in the range of from 25 to 50° C.

In one embodiment, the ionic liquid fed to dissolution zone 20 via line 64 can additionally comprise water, nitrogen-containing bases, alcohol, and/or carboxylic acid. The ionic liquid in line 64 can comprise less than about 15 weight percent, less than about 5 weight percent, or less than 2 weight percent of each of water, nitrogen-containing bases, alcohol, and carboxylic acid.

As mentioned above, an ionic liquid comprises ions. These ions include both cations (i.e., positively charged ions) and anions (i.e., negatively charged ions). In one embodiment, the cations of the ionic liquid suitable for use in the present invention can include, but are not limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations, which correspond to the following structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃, R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂ to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxy group. In one embodiment, the cation of the ionic liquid used in the present invention can comprise an alkyl substituted imidazolium cation, where R₁ is a C₁ to C₄ alkyl group, and R₂ is a different C₁ to C₄ alkyl group.

In one embodiment of the present invention, the cellulose dissolving ionic liquid can be a carboxylated ionic liquid. As used herein, the term “carboxylated ionic liquid” shall denote any ionic liquid comprising one or more carboxylate anions. Carboxylate anions suitable for use in the carboxylated ionic liquids of the present invention include, but are not limited to, C₁ to C₂₀ straight- or branched-chain, substituted or unsubstituted carboxylate anions. Examples of suitable carboxylate anions for use in the carboxylated ionic liquid include, but are not limited to, formate, acetate, propionate, butyrate, valerate, hexanoate, lactate, oxalate, or chloro-, bromo-, fluoro-substituted acetate, propionate, or butyrate, and the like. In one embodiment, the anion of the carboxylated ionic liquid can be a C₂ to C₆ straight-chain carboxylate. Furthermore, the anion can be acetate, propionate, butyrate, or a mixture of acetate, propionate, and/or butyrate. Specific examples of carboxylated ionic liquids suitable for use in the present invention include, but are not limited t, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium propionate, 1-ethyl-3-methylimidazolium butyrate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium propionate, 1-butyl-3-methylimidazolium butyrate, or mixtures thereof.

In one embodiment of the present invention, the carboxylated ionic liquid can contain sulfur in an amount less than 200 parts per million by weight (“ppmw”), less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total weight of the ion content of the carboxylated ionic liquid. Additionally, the carboxylated ionic liquid can contain a total halide content of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total weight of the ion content of the carboxylated ionic liquid. Furthermore, the carboxylated ionic liquid can contain a total metal content of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total weight of the ion content of the carboxylated ionic liquid. In one embodiment, the carboxylated ionic liquid can contain transition metals in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw based on the total weight of the ion content of the carboxylated ionic liquid. The sulfur, halide, and metal content of the carboxylated ionic liquid can be determined by x-ray fluorescence (“XRF”) spectroscopy.

The carboxylated ionic liquid of the present invention can be formed by any process known in the art for making ionic liquids having at least one carboxylate anion. In one embodiment, the carboxylated ionic liquid of the present invention can be formed by first forming an intermediate ionic liquid. The intermediate ionic liquid can be any known ionic liquid, at least a portion of whose ions can participate in an anion exchange reaction. In one embodiment, the intermediate ionic liquid can comprise a plurality of cations such as those described above with reference to the cellulose dissolving ionic liquid (e.g., imidazolium, pyrazolium, oxazolium, 1,2,3,-triazolium, 1,2,4-triazolium, or thiazolium). In one embodiment, the cation of the intermediate ionic liquid can comprise 1-ethyl-3-methylimidazolium or 1-butyl-3-methylimidazolium. Additionally, the intermediate ionic liquid can comprise a plurality of anions. In one embodiment, the intermediate ionic liquid can comprise a plurality of carboxylate anions, such as, for example, formate, acetate, and/or propionate anions.

In one embodiment, the intermediate ionic liquid of the present invention can comprise an alkyl amine formate. The amine cation of the alkyl amine formate can comprise any of the above-described substituted or unsubstituted imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. In one embodiment, the amine of the alkyl amine formate can be an alkyl substituted imidazolium, alkyl substituted pyrazolium, alkyl substituted oxazolium, alkyl substituted triazolium, alkyl substituted thiazolium, and mixtures thereof. In one embodiment, the amine of the alkyl amine formate can be an alkyl substituted imidazolium. Examples of alkyl amine formates suitable for use as an intermediate ionic liquid in the present invention include, but are not limited to, 1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, 1-pentyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazolium formate.

The intermediate ionic liquid useful in the present invention can be formed by contacting at least one amine with at least one alkyl formate. Amines suitable for use in the present invention include, but are not limited to, substituted or unsubstituted imidazoles, pyrazoles, oxazoles, triazoles, and/or thiazoles. In one embodiment, the alkyl amine formate can be formed by contacting at least one alkyl substituted imidazole with at least one alkyl formate. Examples of alkyl substituted imidazoles suitable for use in forming the intermediate ionic liquid include, but are not limited to, 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, and/or 1-octylimidazole. Examples of alkyl formates suitable for use in forming the intermediate ionic liquid include, but are not limited to, methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, tert-butyl formate, hexyl formate, octyl formate, and the like. In one embodiment, the alkyl formate used in forming the intermediate ionic liquid can comprise methyl formate.

Once the intermediate ionic liquid has been formed, the intermediate ionic liquid can be contacted with one or more carboxylate anion donors at a contact time, pressure, and temperature sufficient to cause the at least partial conversion of the intermediate ionic liquid to at least one of the above-mentioned carboxylated ionic liquids. Such conversion can be accomplished via anion exchange between the carboxylate anion donor and the intermediate ionic liquid. In one embodiment, at least a portion of the formate of the alkyl amine formate can be replaced via anion exchange with a carboxylate anion originating from one or more carboxylate anion donors.

Carboxylate anion donors useful in the present invention can include any substance capable of donating at least one carboxylate anion. Examples of carboxylate anion donors suitable for use in the present invention include, but are not limited to, carboxylic acids, anhydrides, and/or alkyl carboxylates. In one embodiment, the carboxylate anion donor can comprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic acids, anhydrides, or methyl esters. Additionally, the carboxylate anion donor can comprise one or more C₂ to C₁₂ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. Furthermore, the carboxylate anion donor can comprise one or more C₂ to C₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. In one embodiment, the carboxylate anion donor can comprise at least one anhydride, which can comprise acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, isophthalic anhydride, and mixtures thereof.

The amount of carboxylate anion donor useful in the present invention can be any amount suitable to convert at least a portion of the intermediate ionic liquid to a carboxylated ionic liquid. In one embodiment, the carboxylate anion donor can be present in a molar ratio with the intermediate ionic liquid in the range of from about 1:1 to about 20:1 carboxylate anion donor-to-intermediate ionic liquid anion content, or in the range of from 1:1 to 6:1 carboxylate anion donor-to-intermediate ionic liquid anion content. In one embodiment, when alkyl amine formate is present as the intermediate ionic liquids, the carboxylate anion donor can be present in an amount in the range of from 1 to 20 molar equivalents per alkyl amine formate, or in the range of from 1 to 6 molar equivalents per alkyl amine formate.

The anion exchange between the intermediate ionic liquid and the carboxylate anion donor can be accomplished in the presence of at least one alcohol. Alcohols useful in the present invention include, but are not limited to, alkyl or aryl alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol, and the like. In one embodiment, the alcohol can be methanol. The amount of alcohol present in the contact mixture during conversion of the intermediate ionic liquid can be in the range of from about 0.01 to about 20 molar equivalents of the ionic liquid, or in the range of from 1 to 10 molar equivalents of the ionic liquid.

In one embodiment, water can be present in the contact mixture during the anion exchange between the intermediate ionic liquid and the carboxylate anion donor. The amount of water present in the contact mixture during conversion of the intermediate ionic liquid can be in the range of from about 0.01 to about 20 molar equivalents of the ionic liquid, or in the range of from 1 to 10 molar equivalents of the ionic liquid.

As mentioned above, the conversion of the intermediate ionic liquid to the carboxylated ionic liquid can be performed at a contact time, pressure, and temperature sufficient to cause the at least partial conversion of the intermediate ionic liquid to the carboxylated ionic liquid. In one embodiment, the conversion can be performed for a time in the range of from about 1 minute to about 24 hours, or in the range of from 30 minutes to 18 hours. Additionally, the conversion can be performed at a pressure up to 21,000 kPa, or up to 10,000 kPa. In one embodiment, the conversion can be performed at a pressure in the range of from about 100 to about 21,000 kPa, or in the range of from 100 to 10,000 kPa. Furthermore, the conversion can be performed at a temperature in the range of from about 0 to about 200° C., or in the range of from 25 to 170° C.

In one embodiment, the resulting carboxylated ionic liquid can comprise carboxylate anions comprising substituted or unsubstituted C₁ to C₂₀ straight- or branched-chain carboxylate anions. In one embodiment, the carboxylate anions can comprise C₂ to C₆ straight-chain carboxylate anions. Additionally, the carboxylated ionic liquid can comprise carboxylate anions such as, for example, formate, acetate, propionate, butyrate, valerate, hexanoate, lactate, and/or oxalate anions. In one embodiment, the carboxylated ionic liquid can comprise at least 50 percent carboxylate anions, at least 70 percent carboxylate anions, or at least 90 percent carboxylate anions. In another embodiment, the carboxylated ionic liquid can comprise at least 50 percent acetate anions, at least 70 percent acetate anions, or at least 90 percent acetate anions.

In an alternative embodiment of the present invention, the above-mentioned cellulose dissolving ionic liquid can be a halide ionic liquid. As used herein, the term “halide ionic liquid” shall denote any ionic liquid that contains at least one halide anion. In one embodiment, the halide anions of the halide ionic liquid can comprise fluoride, chloride, bromide, and/or iodide. In another embodiment, the halide anions can be chloride and/or bromide. Additionally, as mentioned above, the cations of the cellulose dissolving ionic liquid can include, but are not limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations. Any method known in the art suitable for making a halide ionic liquid can be employed in the present invention. Examples of halide ionic liquids suitable for use in the present invention include, but are not limited to, 1-butyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, or mixtures thereof.

Referring again to FIG. 1, the amount of cellulose fed to dissolution zone 20 can be in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 25 weight percent, or in the range of from 10 to 20 weight percent based on the combined weight of cellulose and the total amount of ionic liquid fed to dissolution zone 20. In one embodiment, the resulting medium formed in dissolution zone 20 (a.k.a., the dissolution medium) can comprise other components, such as, for example, water, alcohol, acylating reagents, and/or carboxylic acids. In one embodiment, the medium formed in dissolution zone 20 can comprise water in an amount in the range of from about 0.001 to about 200 weight percent, in the range of from about 1 to about 100 weight percent, or in the range of from 5 to 15 weight percent based on the entire weight of all other components in the medium formed in dissolution zone 20. Additionally, the medium formed in dissolution zone 20 can comprise a total concentration of alcohol in an amount in the range of from about 0.001 to about 200 weight percent, in the range of from about 1 to about 100 weight percent, or in the range of from 5 to 15 weight percent based on the entire weight of all other components in the medium formed in dissolution zone 20.

The medium formed in dissolution zone 20 can optionally comprise one or more co-solvents. In one embodiment, the co-solvent employed can be miscible or soluble with the medium formed in dissolution zone 20. Furthermore, in one embodiment the co-solvent does not act as a catalyst for esterification of cellulose, including the esterification processes described in greater detail below. The medium formed in dissolution zone 20 can comprise a total concentration of co-solvents in the range of from about 0.01 to about 25 weight percent, in the range of from about 0.05 to about 15 weight percent, or in the range of from 0.1 to 5 weight percent based on the total concentration of ionic liquid in the medium formed in dissolution zone 20. In one embodiment, the co-solvent can comprise one or more carboxylic acids. Examples of suitable carboxylic acids useful in this embodiment include, but are not limited to, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and isophthalic acid. In one embodiment, the carboxylic acid in the medium formed in dissolution zone 20 can comprise acetic acid, propionic acid, and/or butyric acid.

In another embodiment, the co-solvent employed can comprise one or more anhydrides. When one or more anhydrides are employed as co-solvents in the medium formed in dissolution zone 20, the total amount of co-solvent present can be in the range of from about 0.01 to about 20 molar equivalents, in the range of from about 0.5 to about 10 molar equivalents, or in the range of from 1.8 to about 4 molar equivalents based on the total amount of cellulose in the medium in dissolution zone 20.

As is described in more detail below with reference to FIG. 2, at least a portion of the carboxylic acids present in the medium formed in dissolution zone 20 can originate from a recycled carboxylated ionic liquid introduced via line 70. Though not wishing to be bound by theory, the inventors have unexpectedly found that the presence of one or more carboxylic acids in the medium in dissolution zone 20 appears to reduce the melting points of the ionic liquids employed, thereby allowing processing of the ionic liquids at lower temperatures than predicted. Additionally, it appears that the use of carboxylic acid in the medium formed in dissolution zone 20 can reduce the viscosity of the cellulose-ionic liquid solution, thereby enabling easier processing of the solution. While the use of a co-solvent can reduce the viscosity of the cellulose-ionic liquid solution, the viscosity of the cellulose-ionic liquid solution can still vary significantly depending on a number of factors, such as the type of ionic liquid employed, the DP of the cellulose, the amount of cellulose in the solution, and the amount of co-solvent present in the solution. Table 1, below, provides viscosity ranges for several different cellulose-ionic liquid solutions at 0.1 rad/sec and a temperature of about 25° C., where each solution has a cellulose concentration of about 5 weight percent and a co-solvent concentration ranging from about 0.01 to about 25 weight percent, but where each solution has various ionic liquid types and cellulose DP values.

TABLE 1 Viscosities of Co-solvent-containing Cellulose-Ionic Liquid Solutions Ionic Liquid Viscosity Type Cellulose DP (poise) [BMIm]Cl 1,090 <60,000 [AMIm]Cl 1,090 <140,000 [BMIm]OAc 1,090 <7,000 [EMIm]OAc 1,090 <3,000 [BMIm]Cl 335 <650 [AMIm]Cl 335 <1,200 When the co-solvent present in the cellulose-ionic liquid solution is an anhydride (as mentioned above), the viscosity can be lowered to a similar degree. Thus, by way of illustration, cellulose-ionic liquid solutions having an anhydride concentration in the range of from about 0.01 to about 20 molar equivalents based on the total amount of cellulose in the ionic liquid, and also having a cellulose concentration of about 5 weight percent can have the same viscosity values as those reported in Table 1, above, at 0.1 rad/sec and a temperature of about 25° C.

In addition to the above, in one embodiment, a cellulose-ionic liquid solution comprising in the range of from about 0.01 to about 25 weight percent of a co-solvent can have a viscosity that is at least 1, at least 5, at least 10, or at least 20 percent lower than the viscosity of the same cellulose-ionic liquid solution without any co-solvent. Additionally, when the co-solvent employed is an anhydride present in the range of from about 0.01 to about 20 molar equivalents based on the total amount of cellulose in the ionic liquid, a co-solvent-containing cellulose-ionic liquid solution can have a viscosity that is at least 1, at least 5, at least 10, or at least 20 percent lower than the viscosity of the same cellulose-ionic liquid solution without any co-solvent.

In one embodiment, the medium formed in dissolution zone 20 can optionally comprise one or more immiscible, substantially immiscible, insoluble, or sparingly soluble co-solvents. As used herein, the terms “substantially immiscible” and “sparingly soluble,” when used in conjunction with a co-solvent, shall denote a co-solvent capable of forming no more than a 1 weight percent solution with the chosen primary solvent (e.g., a cellulose dissolving ionic liquid). Such co-solvents can comprise one or more components that are immiscible or sparingly soluble with the cellulose-ionic liquid medium formed in dissolution zone 20. Surprisingly, the addition of an immiscible or sparingly soluble co-solvent does not cause precipitation of the cellulose upon contacting the medium formed in dissolution zone 20. However, upon contact with an acylating reagent, as will be discussed in more detail below, the cellulose can be esterified, which can in turn alter the solubility of the now cellulose ester-ionic liquid solution with respect to the formerly immiscible or sparingly soluble co-solvent such that the co-solvent can be miscible or soluble with the esterified medium. Accordingly, subsequent to esterification, the contact mixture can become a single phase or highly dispersed mixture containing cellulose ester, ionic liquid, and co-solvent.

The inventors have surprisingly discovered that the resulting single phase or highly dispersed esterified medium appears to have a lower solution viscosity than the initial cellulose-ionic liquid solution. This discovery is significant in that heretofore highly viscous cellulose solutions can now be used to make cellulose esters while still maintaining the ability to mix and process the solution. This discovery also provides a viable method to process highly viscous cellulose-ionic liquid solutions at lower contact temperatures. Accordingly, in one embodiment, an esterified medium (such as the esterified medium in line 80, described in more detail below) can have a viscosity that is at least 1 percent, at least 5 percent, or at least 10 percent lower than the viscosity of the medium formed in dissolution zone 20.

Immiscible or sparingly soluble co-solvents suitable for use in the present invention can comprise alkyl or aryl esters, ketones, alkyl halides, hydrophobic ionic liquids, and the like. Specific examples of immiscible or sparingly soluble co-solvents include, but are not limited to, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate, methyl butyrate, acetone, methyl ethyl ketone, chloroform, methylene chloride, alkyl imidazolium hexafluorophosphate, alkyl imidazolium triflimide, and the like. In one embodiment, the immiscible or sparingly soluble co-solvents can comprise methyl acetate, methyl propionate, methyl butyrate, methyl ethyl ketone, and/or methylene chloride. The weight ratio of immiscible or sparingly soluble co-solvents to cellulose-ionic liquid mixture can be in the range of from about 1:20 to about 20:1, or in the range of from 1:5 to 5:1.

The medium formed in dissolution zone 20 can optionally comprise an acylating reagent, as is discussed in more detail below. The optional acylating reagent can be introduced into dissolution zone 20 via line 78. In one embodiment, the medium formed in dissolution zone 20 can comprise acylating reagent in an amount in the range of from about 0.01 to about 20 molar equivalents, in the range of from about 0.5 to about 10 molar equivalents, or in the range of from 1.8 to about 4 molar equivalents based on the total amount of cellulose in the medium in dissolution zone 20. As will be discussed in more detail below, in certain cases the amount of acylating reagent can be minimized in relation to the amount of cellulose employed.

The medium formed in dissolution zone 20 can also comprise recycled ionic liquid, as is discussed in more detail below with reference to FIG. 2. The recycled ionic liquid can be introduced into dissolution zone 20 via line 70. The medium formed in dissolution zone 20 can comprise recycled ionic liquid in an amount in the range of from about 0.01 to about 99.99 weight percent, in the range of from about 10 to about 99 weight percent, or in the range of from 90 to 98 weight percent based on the total amount of ionic liquid in dissolution zone 20.

In one embodiment, the cellulose entering dissolution zone 20 via line 62 can initially be dispersed in the ionic liquid. Dispersion of the cellulose in the ionic liquid can be achieved by any means known in the art. In one embodiment, dispersion of the cellulose can be achieved by mechanical mixing, such as mixing by one or more mechanical homogenizers.

After the cellulose has been dispersed in the ionic liquid, dissolution of the cellulose in dissolution zone 20, along with removal of at least a portion of any volatile components in the mixture, can be achieved using any method known in the art. For example, dissolution of the cellulose can be achieved by lowering the pressure and/or raising the temperature of the cellulose-ionic liquid dispersion initially formed in dissolution zone 20. Accordingly, after the cellulose is dispersed in the ionic liquid, the pressure can be lowered in dissolution zone 20. In one embodiment, the pressure in dissolution zone 20 can be lowered to less than about 100 millimeters mercury (“mm Hg”), or less than 50 mm Hg. Additionally, the cellulose-ionic liquid dispersion can be heated to a temperature in the range of from about 60 to about 100° C., or in the range of from 70 to 85° C.

After dissolution, the resulting solution can be maintained at the above-described temperatures and pressures for a time in the range of from about 0 to about 100 hours, or in the range of from 1 to 4 hours. The cellulose solution formed in dissolution zone 20 can comprise dissolved cellulose in an amount of at least 10 weight percent based on the entire weight of the solution. In another embodiment, the cellulose solution formed in dissolution zone 20 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, or in the range of from 5 to 20 weight percent, based on the entire weight of the solution.

Following dissolution, at least a portion of the resulting cellulose solution can be removed from dissolution zone 20 via line 66 and routed to esterification zone 40. While in esterification zone 40, at least a portion of the cellulose can undergo esterification. In one embodiment, at least one acylating reagent can be employed to aid in esterifying at least a portion of the cellulose. The acylating can be introduced at various points in the process depicted in FIG. 1. In one embodiment, the acylating reagent can be introduced into esterification zone 40 to aid in esterification of the cellulose. Additionally, as mentioned above, the acylating reagent can be introduced into dissolution zone 20. Furthermore, the acylating reagent can be added after the cellulose has been dissolved in the ionic liquid. Optionally, at least a portion of the acylating reagent can be added to the ionic liquid prior to dissolution of the cellulose in the ionic liquid. Regardless of where or when the acylating reagent is added, at least a portion of the cellulose in esterification zone 40 can undergo esterification subsequent to being contacted with the acylating reagent.

As used herein, the term “acylating reagent” shall denote any chemical compound capable of donating at least one acyl group to a cellulose. As used herein, the term “acyl group” shall denote any organic radical derived from an organic acid by the removal of a hydroxyl group. Acylating reagents useful in the present invention can be one or more C₁ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic anhydrides, carboxylic acid halides, diketene, or acetoacetic acid esters. Examples of carboxylic anhydrides suitable for use as acylating reagents in the present invention include, but are not limited to, acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, and isophthalic anhydride. Examples of carboxylic acid halides suitable for use as acylating reagents in the present invention include, but are not limited to, acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl, lauroyl, palmitoyl, and stearoyl chlorides. Examples of acetoacetic acid esters suitable for use as acylating reagents in the present invention include, but are not limited to, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, and tert-butyl acetoacetate. In one embodiment, the acylating reagents can be C₂ to C₉ straight- or branched-chain alkyl carboxylic anhydrides selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, 2-ethylhexanoic anhydride, and nonanoic anhydride.

Referring still to FIG. 1, the reaction medium formed in esterification zone 40 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 25 weight percent, or in the range of from 10 to 20 weight percent, based on the weight of the ionic liquid in the reaction medium. Additionally, the reaction medium formed in esterification zone 40 can comprise ionic liquid in an amount in the range of from about 20 to about 98 weight percent, in the range of from about 30 to about 95 weight percent, or in the range of from 50 to 90 weight percent based on the total weight of the reaction medium. Furthermore, the reaction medium formed in esterification zone 40 can comprise acylating reagent in an amount in the range of from about 1 to about 50 weight percent, in the range of from about 5 to about 30 weight percent, or in the range of from 10 to 20 weight percent based on the total weight of the reaction medium. Furthermore, the reaction medium formed in esterification zone 40 can have a cumulative concentration of nitrogen containing bases and carboxylic acids in an amount less than 15 weight percent, less than 5 weight percent, or less than 2 weight percent. Moreover, the reaction medium formed in esterification zone 40 can comprise any of the above-mentioned co-solvents (i.e., miscible and/or immiscible co-solvents) in an amount in the range of from about 0.01 to about 40 weight percent, in the range of from about 0.05 to about 20 weight percent, or in the range of from 0.1 to 5 weight percent based on the total weight of the reaction medium. In another embodiment, the reaction medium formed in esterification zone 40 can comprise carboxylic acids in a combined amount in the range of from about 0.01 to about 25 weight percent, in the range of from about 0.05 to about 15 weight percent, or in the range of from about 0.1 to 5 weight percent based on the weight of the ionic liquid in the reaction medium.

In one embodiment, the weight ratio of cellulose-to-acylating reagent in esterification zone 40 can be in the range of from about 9:1 to about 1:9, in the range of from about 3:2 to about 1:3, or in the range of from 9:11 to 7:13. In one embodiment, the acylating reagent can be present in esterification zone 40 in an amount less than 5, less than 4, less than 3, or less than 2.7 molar equivalents per anhydroglucose unit in the cellulose.

In one embodiment of the present invention, when a halide ionic liquid is employed as the cellulose dissolving ionic liquid, a limited excess of acylating reagent can be employed during esterification of the cellulose to achieve a cellulose ester with a particular DS. Thus, in one embodiment, less than 20 percent molar excess, less than 10 percent molar excess, less than 5 percent molar excess, or less than 1 percent molar excess of acylating reagent can be employed during esterification.

Optionally, one or more catalysts can be introduced into esterification zone 40 to aid in esterification of the cellulose. The catalyst employed in the present invention can be any catalyst that increases the rate of esterification in esterification zone 40. When a catalyst is employed in esterification zone 40, the catalyst can be added to the cellulose solution prior to adding the acylating reagent, which is discussed in greater detail below. In another embodiment the catalyst can be added to the cellulose solution as a mixture with the acylating reagent.

In one embodiment, the catalyst employed in the present invention can be an acidic component. In one embodiment, the acidic component employed in esterification zone 40 can comprise one or more protic acids. As used herein, the term “protic acid” shall denote any acid capable of donating at least one proton. Protic acids suitable for use in the present invention can have a pK_(a) value in the range of from about −5 to about 10, or in the range of from −2.5 to 2.0. Protic acids suitable for use in the present invention can include sulfuric acid, alkyl sulfonic acids, and aryl sulfonic acids. Specific examples of protic acids suitable for use in the present invention include, but are not limited to, methane sulfonic acid (“MSA”), p-toluene sulfonic acid, and the like.

In another embodiment, the acidic component employed in esterification zone 40 can be one or more Lewis acids. Lewis acids suitable for use as the acidic component in esterification zone 40 can be of the type MX_(n), where M is a transition metal exemplified by B, Al, Fe, Ga, Sb, Sn, As, Zn, Mg, or Hg, and X is halogen, carboxylate, sulfonate, alkoxide, alkyl, or aryl. Examples of Lewis acids suitable for use as catalysts include, but are not limited to, ZnCl₂, Zn(OAc)₂, and the like.

Additionally, functional ionic liquids can be employed as catalysts during esterification of the cellulose. Functional ionic liquids are ionic liquids containing specific functional groups, such as hydrogen sulfonate, alkyl or aryl sulfonates, and carboxylates, that effectively catalyze the esterification of cellulose using an acylating reagent. Examples of functional ionic liquids include 1-alkyl-3-methylimidazolium hydrogen sulfate, methyl sulfonate, tosylate, and trifluoroacetate, where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group. Additionally, suitable functional ionic liquids for use in the present invention are those in which the functional group is covalently linked to the cation.

An example of a covalently-linked functional ionic liquid suitable for use in the present invention includes, but is not limited to, the following structure:

where at least one of the R₁, R₂, R₃, R₄, R₅ groups are replaced with the group (CHX)_(n)Y, where X is hydrogen or halide, n is an integer in the range of from 1 to 10, and Y is sulfonic or carboxylate, and the remainder R₁, R₂, R₃, R₄, R₅ groups are those previously described in relation to the cations suitable for use as the cellulose dissolving ionic liquid. Examples of covalently-linked functional ionic liquids suitable for use in the present invention include, but are not limited to, 1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluorobutyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium, 1-alkyl-3-(1-sulfonylethyl)imidazolium, 1-alkyl-3-(1-sulfonylpropyl)imidazolium, 1-alkyl-3-(1-sulfonylbutyl)imidazolium, and 1-alkyl-3-(1-sulfonylhexyl)imidazolium, where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group.

The amount of catalyst used to catalyze the esterification of cellulose may vary depending upon the type of catalyst employed, the type of acylating reagent employed, the type of ionic liquid, the contact temperature, and the contact time. Thus, a broad concentration of catalyst employed is contemplated by the present invention. In one embodiment, the amount of catalyst employed in esterification zone 40 can be in the range of from about 0.01 to about 30 mol percent catalyst per anhydroglucose unit (“AGU”), in the range of from about 0.05 to about 10 mol percent catalyst per AGU, or in the range of from 0.1 to 5 mol percent catalyst per AGU. In one embodiment, the amount of catalyst employed can be less than 30 mol percent catalyst per AGU, less than 10 mol percent catalyst per AGU, less than 5 mol percent catalyst per AGU, or less than 1 mol percent catalyst per AGU.

The inventors have discovered a number of surprising and unpredictable advantages apparently associated with employing a catalyst as a binary component (e.g., acidic component, functional ionic liquid) during the esterification of cellulose. For example, the inventors have discovered that the inclusion of a binary component can accelerate the rate of esterification. Very surprisingly, the binary component can also serve to improve solution and product color, prevent gelation of the esterification mixture, provide increased DS values in relation to the amount of acylating reagent employed, and/or help to decrease the molecular weight of the cellulose ester product. In one embodiment, when a catalyst is employed as a binary component, the amount of binary component employed can be in the range of from about 0.01 to about 100 mol percent per AGU, in the range of from about 0.05 to about 20 mol percent per AGU, or in the range of from 0.1 to 5 mol percent per AGU.

In addition to the above, it has been discovered that the use of a binary component can lower the viscosity of the reaction medium in esterification zone 40. Accordingly, when the initial medium formed in esterification zone 40 comprises 1-butyl-3-methylimidazolium chloride as the ionic liquid, one or more binary components in a total amount in the range of from about 0.01 to about 100 mol percent per AGU, and cellulose having a DP of about 1,090 in an amount of at least 5 weight percent, the medium can have a viscosity of less than about 60,000 poise at 0.1 rad/sec at a temperature of about 25° C. Furthermore, when the initial medium formed in esterification zone 40 comprises 1-allyl-3-methylimidazolium chloride as the ionic liquid, one or more binary components in a total amount in the range of from about 0.01 to about 100 mol percent per AGU, and cellulose having a DP of about 1,090 in an amount of at least 5 weight percent, the medium can have a viscosity of less than about 140,000 poise at 0.1 rad/sec at a temperature of about 25° C. Additionally, when the medium formed in esterification zone 40 comprises 1-butyl-3-methylimidazolium chloride as the ionic liquid, one or more binary components in an amount in the range of from about 0.01 to about 100 mol percent per AGU, and cellulose having a DP of about 335 in an amount of at least 5 weight percent, the medium can have a viscosity of less than about 650 poise at 0.1 rad/sec at a temperature of about 25° C. Moreover, when the medium formed in esterification zone 40 comprises 1-allyl-3-methylimidazolium chloride as the ionic liquid, one or more binary components in an amount in the range of from about 0.01 to about 100 mol percent per AGU, and cellulose having a DP of about 335 in an amount of at least 5 weight percent, the medium can have a viscosity of less than about 650 poise at 0.1 rad/sec at a temperature of about 25° C.

It should be noted that binary components suitable to be employed in the present invention are not limited to catalysts such as acidic components or functional ionic liquids. Rather, as used herein, the term “binary component” shall denote any non-cellulosic substance that, upon addition to the ionic liquid, alters the network structure of the ionic liquid. By way of illustration, the structure of an exemplary ionic liquid network appears as follows:

As can be seen from the above structure, an ionic liquid can comprise a network of ionically linked anions and cations. However, upon addition of a binary component this network may become disrupted. This change in network structure may lead to the observed surprising and unpredicted advantages of using a binary component.

As mentioned above, at least a portion of the cellulose can undergo an esterification reaction in esterification zone 40. The esterification reaction carried out in esterification zone 40 can operate to convert at least a portion of the hydroxyl groups present on the cellulose to ester groups, thereby forming a cellulose ester. As used herein, the term “cellulose ester” shall denote a cellulose polymer having at least one ester substituent. In one embodiment, at least a portion of the ester groups on the resulting cellulose ester can originate from the above-described acylating reagent. The cellulose esters thus prepared can comprise the following structure:

where R₂, R₃, and R₆ can independently be hydrogen, so long as R₂, R₃, and R₆ are not all hydrogen simultaneously on every AGU, or C₁ to C₂₀ straight- or branched-chain alkyl or aryl groups bound to the cellulose via an ester linkage.

In one embodiment, when the ionic liquid employed is a carboxylated ionic liquid, one or more of the ester groups on the resulting cellulose ester can originate from the ionic liquid in which the cellulose is dissolved. Additionally, the ester group(s) on the cellulose ester originating from the carboxylated ionic liquid can be a different ester group than the ester group(s) on the cellulose ester that originates from the acylating reagent. Though not wishing to be bound by theory, it is believed that when an acylating reagent is introduced into a carboxylated ionic liquid, an anion exchange can occur such that one or more carboxylate anions originating from the acylating reagent replace at least a portion of the carboxylate anions originally in the carboxylated ionic liquid, thereby creating an altered ionic liquid, which is discussed in more detail below. When the carboxylate anions originating from the acylating reagent are of a different type than the carboxylate anions of the ionic liquid, then the altered ionic liquid can comprise at least two different types of carboxylate anions. Thus, so long as the carboxylate anions from the carboxylated ionic liquid comprise a different acyl group than is found on the acylating reagent, at least two different acyl groups are available for esterification of the cellulose. By way of illustration, if cellulose was dissolved in 1-butyl-3-methylimidazolium acetate (“[BMIm]OAc” or “[BMIm]acetate”) and a propionic anhydride (“Pr₂O”) acylating reagent was added to the carboxylated ionic liquid, the carboxylated ionic liquid can become an altered ionic liquid, comprising a mixture of [BMIm]acetate and [BMIm]propionate. Thus, the process of forming a cellulose ester under these conditions can be illustrated as follows:

As illustrated, contacting a solution of cellulose dissolved in [BMIm]acetate with a propionic anhydride can result in the formation of a cellulose ester comprising both acetate ester substituents and propionate ester substituents. Thus, as mentioned above, at least a portion of the ester groups on the cellulose ester can originate from the ionic liquid, and at least a portion of the ester groups can originate from the acylating reagent. When this scenario occurs, the amount of ester groups on the resulting cellulose ester that originate from the carboxylated ionic liquid can be at least 10 percent, at least 25 percent, at least 50 percent, or at least 75 percent of the total number of ester groups on the resulting cellulose ester. Additionally, at least one of the ester groups donated by the ionic liquid can be an acyl group. In one embodiment, all of the ester groups donated by the ionic liquid can be acyl groups.

Therefore, in one embodiment, the cellulose ester prepared by methods of the present invention can be a mixed cellulose ester. As used herein, the term “mixed cellulose ester” shall denote a cellulose ester having at least two different ester substituents on a single cellulose ester polymer chain. The mixed cellulose ester of the present invention can comprise a plurality of first pendant acyl groups and a plurality of second pendant acyl groups, where the first pendant acyl groups originate from the ionic liquid, and the second pendant acyl groups originate from the acylating reagent. In one embodiment, the mixed cellulose ester can comprise a molar ratio of at least two different pendant acyl groups in the range of from about 1:10 to about 10:1, in the range of from about 2:8 to about 8:2, or in the range of from 3:7 to 7:3. Additionally, the first and second pendant acyl groups can individually comprise acetyl, propionyl, butyryl, isobutyryl, valeryl, hexanoyl, 2-ethylhexanoyl, nonanoyl, lauroyl, palmitoyl, benzoyl, substituted benzoyl, phthalyl, isophthalyl, and/or stearoyl groups. In one embodiment, the first and second pendant acyl groups individually comprise acetyl, propionyl, and/or butyryl groups.

In one embodiment, at least one of the first pendant acyl groups can be donated by the ionic liquid or at least one of the second pendant acyl groups can be donated by the ionic liquid. As used herein, the term “donated,” with respect to esterification, shall denote a direct transfer of an acyl group. Comparatively, the term “originated,” with respect to esterification, can signify either a direct transfer or an indirect transfer of an acyl group. In one embodiment of the invention, at least 50 percent of the above-mentioned first pendant acyl groups can be donated by the ionic liquid, or at least 50 percent of the second pendant acyl groups can be donated by the ionic liquid. Furthermore, at least 10 percent, at least 25 percent, at least 50 percent, or at least 75 percent of all of the pendant acyl groups on the resulting cellulose ester can result from donation of acyl groups by the ionic liquid.

In one embodiment, the above-described mixed cellulose ester can be formed by a process where a first portion of the first pendant acyl groups can initially be donated from the acylating reagent to the carboxylated ionic liquid, and then the same acyl groups can be donated from the carboxylated ionic liquid to the cellulose (i.e., indirectly transferred from the acylating reagent to the cellulose, via the ionic liquid). Additionally, a second portion of the first pendant acyl groups can be donated directly from the acylating reagent to the cellulose.

Referring again to FIG. 1, the temperature in esterification zone 40 during the above-described esterification process can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 80° C., or in the range of from 25 to 50° C. Additionally, the cellulose can have a residence time in esterification zone 40 in the range of from about 1 minute to about 48 hours, in the range of from about 30 minutes to about 24 hours, or in the range of from 1 to 5 hours.

Following the above-described esterification process, an esterified medium can be withdrawn from esterification zone 40 via line 80. The esterified medium withdrawn from esterification zone 40 can comprise an initial cellulose ester. In one embodiment, the initial cellulose ester in line 80 can be a non-random cellulose ester. As used herein, the term “non-random cellulose ester” shall denote a cellulose ester having a non-Gaussian distribution of substituted monomers as determined by NMR spectroscopy. Additionally, the initial cellulose ester in line 80 can be a mixed cellulose ester, as described above.

The initial cellulose ester can have a degree of substitution (“DS”) in the range of from about 0.1 to about 3.0, in the range of from about 1.8 to about 2.9, or in the range of from 2.0 to 2.6. In another embodiment, the initial cellulose ester can have a DS of at least 2. In yet another embodiment, the initial cellulose ester can have a DS of less than 3.0, or less than 2.9.

In another embodiment, when a binary component is employed in esterification zone 40, at least 50, at least 60, or at least 70 percent of the ester substituents on the initial cellulose ester can comprise alkyl esters having a carbon chain length at least 6 carbon atoms long, at least 7 carbon atoms long, or at least 8 carbon atoms long. Additionally, the average ester substituent chain length of the initial cellulose ester can be at least 6 carbon atoms long, at least 7 carbon atoms long, or at least 8 carbon atoms long. In this embodiment, the initial cellulose ester can have a DS of at least 1.5, at least 1.7, or at least 2.0.

As mentioned above, in another embodiment a limited excess of acylating reagent can be employed during esterification in esterification zone 40. For example, a molar excess of less than 20 percent, less than 10 percent, less than 5 percent, or less than 1 percent of acylating reagent can be employed during esterification. In this embodiment, the resulting initial cellulose ester can have a DS of at least 1.8, or at least 2.0.

The degree of polymerization (“DP”) of the cellulose esters prepared by the methods of the present invention can be at least 10, at least 50, at least 100, or at least 250. In another embodiment, the DP of the initial cellulose ester can be in the range of from about 5 to about 1,000, or in the range of from 10 to 250.

In addition to the initial cellulose ester, the esterified medium in line 80 can comprise altered ionic liquid, residual acylating reagent, one or more carboxylic acids, and/or residual binary component. As used herein and as is discussed in more detail below, the term “altered ionic liquid” refers to an ionic liquid that has previously passed through a cellulose esterification step wherein at least a portion of the ionic liquid acted as an acyl group donor and/or recipient. The esterified medium in line 80 can comprise the initial cellulose ester in an amount in the range of from about 2 to about 80 weight percent, in the range of from about 10 to about 60 weight percent, or in the range of from 20 to 40 weight percent based on the total weight of ionic liquid in the esterified medium. In one embodiment, the esterified medium in line 80 can comprise altered ionic liquid in an amount in the range of from about 0.01 to about 99.99 weight percent, in the range of from about 10 to about 99 weight percent, or in the range of from 90 to 98 weight percent relative to the amount of initial ionic liquid introduced into dissolution zone 20. Additionally, the esterified medium in line 80 can comprise residual acylating reagent in an amount less than about 20 weight percent, less than about 10 weight percent, or less than 5 weight percent.

Furthermore, the esterified medium in line 80 can comprise a total concentration of carboxylic acids in an amount in the range of from about 0.01 to about 40 weight percent, in the range of from about 0.05 to about 20 weight percent, or in the range of from 0.1 to 5 weight percent. In another embodiment, the esterified medium in line 80 can comprise a total concentration of carboxylic acids in an amount less than 40, less than 20, or less than 5 weight percent. Carboxylic acids that can be present in the esterified medium in line 80 include, but are not limited to, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and/or isophthalic acid.

In one embodiment of the present invention, the esterified medium in line 80 can be in the form of a solution. In this embodiment, the esterified solution in line 80 can comprise a total concentration of the above-described co-solvents in an amount in the range of from about 0.01 to about 40 weight percent, in the range of from about 0.05 to about 20 weight percent, or in the range of from about 0.1 to 5 weight percent.

Following esterification, the esterified medium in line 80 can be routed to cellulose ester recovery/treatment zone 50. As is discussed in more detail below with reference to FIG. 2, at least a portion of the initial cellulose ester from the esterified medium can optionally be subjected to at least one randomization process in recovery/treatment zone 50, thereby producing a randomized cellulose ester. Additionally, as is discussed in more detail below with reference to FIG. 2, at least a portion of the cellulose ester from the esterified medium can be caused to precipitate out of the esterified medium, at least a portion of which can thereafter be separated from the resulting mother liquor. Furthermore, the separated cellulose ester can then optionally be washed, as is described in more detail below with reference to FIG. 2.

Referring still to FIG. 1, at least a portion of the cellulose ester precipitated and recovered in recovery/treatment zone 50 can be withdrawn via line 90 as a final cellulose ester. The final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a number average molecular weight (“Mn”) in the range of from about 1,200 to about 200,000, in the range of from about 6,000 to about 100,000, or in the range of from 10,000 to 75,000. Additionally, the final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a weight average molecular weight (“Mw”) in the range of from about 2,500 to about 420,000, in the range of from about 10,000 to about 200,000, or in the range of from 20,000 to 150,000. Furthermore, the final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a Z-average molecular weight (“Mz”) in the range of from about 4,000 to about 850,000, in the range of from about 12,000 to about 420,000, or in the range of from 40,000 to 330,000. The final cellulose ester exiting recovery/treatment zone 50 via line 90 can have a polydispersity in the range of from about 1.3 to about 7, in the range of from about 1.5 to about 5, or in the range of from 1.8 to 3. Additionally, the final cellulose ester in line 90 can have a DP and DS as described above in relation to the initial cellulose ester in line 80. Furthermore, the cellulose ester can be random or non-random, as is discussed in more detail below with reference to FIG. 2. Moreover, the final cellulose ester in line 90 can comprise a plurality of ester substituents as described above. Also, the final cellulose ester in line 90 can optionally be a mixed cellulose ester as described above.

In one embodiment, the cellulose ester in line 90 can be in the form of a wet cake. The wet cake in line 90 can comprise a total liquid content of less than 99, less than 50, or less than 25 weight percent. Furthermore, the wet cake in line 90 can comprise a total ionic liquid concentration of less than 1, less than 0.01, or less than 0.0001 weight percent. Additionally, the wet cake in line 90 can comprise a total alcohol content of less than 100, less than 50, or less than 25 weight percent. Optionally, as is discussed in greater detail below with reference to FIG. 2, the final cellulose ester can be dried to produce a dry final cellulose ester product.

The cellulose esters prepared by the methods of this invention can be used in a variety of applications. Those skilled in the art will understand that the specific application in which the cellulose ester is used will depend upon various characteristics of the cellulose ester, such as, for example, the type of acyl substituent, DS, DP, molecular weight, and type of cellulose ester copolymer. In one embodiment of the present invention, the cellulose esters can be used in thermoplastic applications in which the cellulose ester is used to make film or molded objects. Examples of cellulose esters suitable for use in thermoplastic applications include, but are not limited to, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, or mixtures thereof.

In another embodiment of the invention, the cellulose esters can be used in coating applications. Examples of coating applications include but, are not limited to, automotive, wood, plastic, or metal coating processes. Examples of cellulose esters suitable for use in coating applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, or mixtures thereof.

In yet another embodiment of the invention, the cellulose esters can be used in personal care applications. In personal care applications, cellulose esters can be dissolved or suspended in appropriate solvents. The cellulose ester can then act as a structuring agent, delivery agent, and/or film forming agent when applied to skin or hair. Examples of cellulose esters suitable for use in personal care applications include, but are not limited to, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose hexanoate, cellulose 2-ethylhexanoate, cellulose laurate, cellulose palmitate, cellulose stearate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters can be used in drug delivery applications. In drug delivery applications, the cellulose ester can act as a film former, such as in the coating of tablets or particles. The cellulose ester can also be used to form amorphous mixtures of poorly soluble drugs, thereby improving the solubility and bioavailability of the drugs. The cellulose esters can also be used in controlled drug delivery, where the drug can be released from a cellulose ester matrix in response to external stimuli such as a change in pH. Examples of cellulose esters suitable for use in drug delivery applications include, but are not limited to cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, or mixtures thereof.

In a further embodiment of the invention, the cellulose esters of the present invention can be used in applications involving solvent casting of film. Examples of such applications include photographic film and protective film for liquid crystalline displays. Examples of cellulose esters suitable for use in solvent cast film applications include, but are not limited to, cellulose triacetate, cellulose acetate, cellulose propionate, and cellulose acetate propionate.

Referring still to FIG. 1, at least a portion of the mother liquor separated in cellulose ester recovery/treatment zone 50 can be withdrawn via line 86 and routed to ionic liquid recovery/treatment zone 60 as a recycle stream. As will be discussed in further detail below with reference to FIG. 2, the recycle stream can undergo various treatments in ionic liquid recovery/treatment zone 60. Such treatment can include, but is not limited to, volatiles removal and reformation of the ionic liquid. Reformation of the ionic liquid can include, but is not limited to, (1) anion homogenization, and (2) anion exchange. Accordingly, a recycled ionic liquid can be formed in ionic liquid recovery/treatment zone 60.

In the embodiment depicted in FIG. 1, at least a portion of the recycled ionic liquid formed in ionic liquid recovery/treatment zone 60 can be withdrawn via line 70. The recycled ionic liquid in line 70 can have substantially the same composition as the ionic liquid described above with reference to line 64 of FIG. 1. The production and composition of the recycled ionic liquid will be discussed in greater detail below with reference to FIG. 2. As mentioned above, at least a portion of the recycled ionic liquid in line 70 can be routed back to dissolution zone 20. In one embodiment, at least about 80 weight percent, at least about 90 weight percent, or at least 95 weight percent of the recycled ionic liquid produced in ionic liquid recovery/treatment zone 60 can be routed to dissolution zone 20.

Referring now to FIG. 2, a more detailed diagram for the production of cellulose esters is depicted, including optional steps for improving the overall efficacy and/or efficiency of the cellulose ester production process. The process depicted in FIG. 2 includes such additional and/or optional steps as cellulose modification, cellulose ester randomization, precipitation, washing, and drying.

In the embodiment depicted in FIG. 2, cellulose can be introduced into an optional modification zone 110 via line 162. The cellulose fed to optional modification zone 110 can be substantially the same as the cellulose in line 62 described above with reference to FIG. 1. In optional modification zone 110, the cellulose can be modified employing at least one modifying agent. The modifying agent suitable for use in the present invention can be any substance capable of increasing the dispersibility of the cellulose in an ionic liquid.

In one embodiment, the modifying agent employed in modification zone 110 can comprise water. Thus, following modification, a water-wet cellulose can be withdrawn from optional modification zone 110 and added to one or more ionic liquids in dissolution zone 120. In one embodiment, the cellulose can be mixed with water then pumped into one or more ionic liquids as a slurry. Alternatively, excess water can be removed from the cellulose, and thereafter the cellulose can be added to the one or more ionic liquids in the form of a wet cake. In one embodiment, the water-wet cellulose introduced into dissolution zone 120 can comprise water in an amount of at least 10 weight percent, at least 15 weight percent, or at least 20 weight percent based on the combined weight of the cellulose and water. In another embodiment, the cellulose wet cake introduced into dissolution zone 120 can contain water in an amount in the range of from about 10 to about 95 weight percent, in the range of from about 20 to about 80 weight percent, or in the range of from 25 to 75 weight percent, based on the combined weight of the cellulose and water. It should be noted that the type of water employed as a modifying agent is not critical, and can include tap, deionized, and/or purified water.

Though not wishing to be bound by theory, the use of an initially water-wet cellulose in the production of cellulose esters has unexpectedly and unpredictably been found to provide at least three heretofore unknown benefits. First, water appears to increase dispersion of the cellulose in ionic liquids so that when removal of water is initiated while heating the cellulose, the cellulose dissolves more quickly. Second, the presence of water appears to reduce the melting points of ionic liquids, including those that are normally solids at room temperature, thus allowing processing of ionic liquids at ambient temperatures. A third benefit is that the molecular weight of cellulose esters prepared using initially water-wet cellulose is reduced during the above-described esterification process when compared to cellulose esters prepared using initially dry cellulose.

This third benefit is particularly surprising and useful. Under typical cellulose ester processing conditions, the molecular weight of cellulose is not reduced during dissolution or during esterification. That is, the molecular weight of the cellulose ester product is directly proportionate to the molecular weight of the initial cellulose. Typical wood pulps used to prepare cellulose esters generally have a DP in the range of from about 1,000 to about 3,000. However, depending on the end-use application, the desired DP range of cellulose esters can be in the range of from about 10 to about 500. Thus, in the absence of molecular weight reduction during esterification, the cellulose must be specially treated either prior to dissolving the cellulose in the ionic liquid or after dissolving in the ionic liquid but prior to esterification. However, when employing water as at least one of the optional modifying agents, pretreatment of the cellulose is not required since molecular weight reduction can occur during esterification. Accordingly, in one embodiment of the present invention, the DP of the modified cellulose subjected to esterification can be within about 10 percent of, within about 5 percent of, within 2 percent of, or substantially the same as the DP of the initial cellulose subjected to modification, while the DP of the cellulose ester product can have a DP that is less than about 90 percent, less than about 70 percent, or less than 50 percent of the DP of the modified cellulose subjected to esterification.

Referring still to FIG. 2, the optionally modified cellulose in line 166 can be introduced into dissolution zone 120. Once in dissolution zone 120, the optionally modified cellulose can be dispersed in one or more ionic liquids in substantially the same manner as described above with reference to dissolution zone 20 in FIG. 1. Subsequently, at least a portion of the modifying agent in the resulting cellulose-ionic liquid mixture can be removed. In one embodiment, at least 50 weight percent, at least 75 weight percent, at least 95 weight percent, or at least 99 weight percent of all modifying agents can be removed from the cellulose-ionic liquid mixture. Removal of the one or more modifying agents from dissolution zone 120 can be accomplished by any means known in the art for liquid/liquid separation, such as, for example, distillation, flash vaporization, and the like. In one embodiment, removal of at least a portion of the one or more modifying agents can be accomplished by lowering the pressure and/or raising the temperature of the cellulose-ionic liquid mixture. Removed modifying agent can be withdrawn from dissolution zone 120 via line 124.

After removal of the modifying agent, dissolution zone 120 can produce a cellulose solution in substantially the same manner as dissolution zone 20, as described above with reference to FIG. 1. However, when a modifying agent is employed for modification of the initial cellulose, dissolution of the modified cellulose in dissolution zone 120 can be carried out for a dissolution period of less than 120 minutes, less than 90 minutes, or less than 60 minutes, while at least 90, at least 95, or at least 99 weight percent of the modified cellulose dissolves during the dissolution period.

Following dissolution, a cellulose solution can be withdrawn from dissolution zone 120 via line 176. The cellulose solution in line 176 can comprise ionic liquid, cellulose, and a residual concentration of one or more optional modifying agents. The cellulose solution in line 176 can comprise cellulose in an amount in the range of from about 1 to about 40 weight percent, in the range of from about 5 to about 30 weight percent, or in the range of from 10 to 20 weight percent, based on the weight of the ionic liquid. Furthermore, the cellulose solution in line 176 can comprise a cumulative amount of residual modifying agents in an amount of less than about 50 weight percent, less than about 25 weight percent, less than about 15 weight percent, less than about 5 weight percent, or less than 1 weight percent.

In the embodiment of FIG. 2, at least a portion of the cellulose solution in line 176 can be introduced into esterification zone 140. Esterification zone 140 can be operated in substantially the same manner as esterification zone 40, as described above with reference to FIG. 1. For example, an acylating reagent can be introduced into esterification zone 140 via line 178. As in esterification zone 40, the acylating reagent can assist in esterifying at least a portion of the cellulose in esterification zone 140. Additionally, as described above, at least a portion of the resulting cellulose ester can comprise one or more ester substituents that originated from and/or were donated by the ionic liquid.

After esterification in esterification zone 140, an esterified medium can be withdrawn via line 180. The esterified medium in line 180 can be substantially the same as the esterified medium in line 80, as described above with reference to FIG. 1. Thus, the esterified medium in line 180 can comprise an initial cellulose ester and other components, such as, for example, altered ionic liquid, residual acylating reagent, one or more carboxylic acids, and/or one or more catalysts. The concentrations of the initial cellulose ester and other components in the esterified medium in line 180 can be substantially the same as the esterified medium in line 80, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above the initial cellulose ester produced in esterification zone 140 can be a non-random cellulose ester. In one embodiment, at least a portion of the initial cellulose in line 180 can optionally be introduced into randomization zone 151 to undergo randomization, thereby creating a random cellulose ester. Randomization of the initial cellulose can comprise introducing at least one randomizing agent into randomization zone 151 via line 181, thereby forming a randomization medium. Additionally, as will be discussed in further detail below, at least a portion of the randomizing agent introduced into randomization zone 151 can be introduced via line 194.

The randomizing agent employed in the present invention can be any substance capable lowering the DS of the cellulose ester via hydrolysis or alcoholysis, and/or capable of causing migration of at least a portion of the acyl groups on the cellulose ester from one hydroxyl to a different hydroxyl, thereby altering the initial monomer distribution. Examples of suitable randomizing agents include, but are not limited to water and/or alcohols. Alcohols suitable for use as the randomizing agent include, but are not limited to, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol and the like. In one embodiment, methanol can be employed as the randomizing agent introduced into randomization zone 151 via line 181.

The amount of randomizing agent introduced into randomization zone 151 can be in the range of from about 0.5 to about 20 weight percent, or in the range of from 3 to 10 weight percent, based on the total weight of the resulting randomization medium in randomization zone 151. The randomization medium can have any residence time in randomization zone 151 suitable to achieve the desired level of randomization of the cellulose ester. In one embodiment, the randomization medium can have a residence time in randomization zone 151 in the range of from about 1 min. to about 48 hours, in the range of from about 30 min. to about 24 hours, or in the range of from 2 to 12 hours. Additionally, the temperature in randomization zone 151 during randomization can be any temperature suitable to achieve the desired level of randomization of the cellulose ester. In one embodiment, the temperature in randomization zone 151 during randomization can be in the range of from about 20 to about 120° C., in the range of from about 30 to about 100° C., or in the range of from 50 to 80° C.

Those skilled in the art will understand that the DS and DP of the random cellulose ester might be less than that of the non-random cellulose ester. Accordingly, in this embodiment the non-random cellulose ester entering randomization zone 151 may optionally have a greater DS and/or DP than the target DS and/or DP of the random cellulose ester.

In one embodiment of the present invention, it may be desirable to produce cellulose esters that are at least partially soluble in acetone. Accordingly, the initial cellulose ester produced in esterification zone 140 can bypass optional randomization zone 151, thereby producing a final non-random cellulose ester. Non-random cellulose esters prepared by the methods of the present invention can be at least partially soluble in acetone when they have a DS in the range of from about 2.0 to about 2.5, in the range of from about 2.1 to about 2.4, in the range of from about 2.28 to about 2.39 or in the range of from 2.32 to 2.37. Additionally, cellulose esters prepared by the methods of the present invention can be sufficiently soluble in acetone to form an at least 1, at least 5, or at least 10 weight percent cellulose ester solution in acetone.

After optional randomization, an optionally randomized medium can be withdrawn from randomization zone 151 via line 182. The optionally randomized medium can comprise a random cellulose ester and residual randomizing agent. In one embodiment, the optionally randomized medium in line 182 can comprise random cellulose ester in an amount in the range of from about 2 to about 80 weight percent, in the range of from about 10 to about 60 weight percent, or in the range of from 20 to 40 weight percent based on the total weight of the ionic liquid in the randomized medium. Additionally, the optionally randomized medium can comprise residual randomizing agent in the range of from about 0.5 to about 20 weight percent, or in the range of from 3 to 10 weight percent, based on the total weight of the resulting randomized medium. The optionally randomized medium in line 182 also can comprise other components, such as those described above with reference to the esterified medium in line 180 and with reference to the esterified medium in line 80 of FIG. 1. Such components include, but are not limited to, altered ionic liquid, residual acylating reagent, one or more carboxylic acids, and/or one or more catalysts.

Following optional randomization, at least a portion of the esterified and optionally randomized medium in line 182 can be introduced into precipitation zone 152. Precipitation zone 152 can operate to cause at least a portion of the cellulose ester from the esterified and optionally randomized medium to precipitate. Any methods known in the art suitable for precipitating a substance out of solution can be employed in precipitation zone 152. In one embodiment, one or more precipitating agents can be introduced into precipitation zone 152 via line 183, thereby causing at least a portion of the cellulose ester to precipitate out of the esterified and optionally randomized medium. Furthermore, as will be discussed in more detail below, at least a portion of the precipitating agent can optionally be introduced into precipitation zone 152 via line 194. In one embodiment, the precipitating agent can be a non-solvent for the cellulose ester. Examples of suitable non-solvents that can be employed as precipitating agents include, but are not limited to, C₁ to C₈ alcohols, water, or mixtures thereof. In one embodiment, the precipitating agent introduced into precipitation zone 152 can comprise methanol.

The amount of precipitating agent introduced into precipitation zone 152 can be any amount sufficient to cause at least a portion of the cellulose ester to precipitate out of the esterified and optionally randomized medium. In one embodiment, the amount of precipitating agent introduced into precipitation zone 152 can be at least about 4 volumes, at least 10 volumes, or at least 20 volumes, based on the total volume of the medium entering precipitation zone 152. The resulting precipitation medium can have any residence time in precipitation zone 152 suitable to achieve the desired level of precipitation. In one embodiment, the precipitation medium can have a residence time in precipitation zone 152 in the range of from about 1 to about 300 min., in the range of from about 10 to about 200 min., or in the range of from 20 to 100 min. Additionally, the temperature in precipitation zone 152 during precipitation can be any temperature suitable to achieve the desired level of precipitation. In one embodiment, the temperature in precipitation zone 152 during precipitation can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 100° C., or in the range of from 25 to 50° C. The amount of cellulose ester precipitated in precipitation zone 152 can be at least 50 weight percent, at least 75 weight percent, or at least 95 weight percent, of the total amount of cellulose ester in precipitation zone 152.

After precipitation in precipitation zone 152, a cellulose ester slurry comprising a final cellulose ester can be withdrawn via line 184. The cellulose ester slurry in line 184 can have a solids content of less than about 50 weight percent, less than about 25 weight percent, or less than 1 weight percent.

At least a portion of the cellulose ester slurry in line 184 can be introduced into separation zone 153. In separation zone 153, at least a portion of the liquid content of the cellulose ester slurry can be separated from the solids portion. Any solid/liquid separation technique known in the art for separating at least a portion of a liquid from a slurry can be used in separation zone 153. Examples of solid/liquid separation techniques suitable for use in the present invention include, but are not limited to, centrifugation, filtration, and the like. Furthermore, separation zone 153 can have any temperature or pressure suitable for solid/liquid separation. In one embodiment, the temperature in separation zone 153 during separation can be in the range of from about 0 to about 120° C., in the range of from about 20 to about 100° C., or in the range of from 25 to 50° C. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the liquid portion of the cellulose ester slurry can be removed in separation zone 153.

After separation in separation zone 153, a cellulose ester wet cake can be withdrawn from separation zone 153 via line 187. Additionally, as will be discussed in greater detail below, at least a portion of the separated liquids from separation zone 153 can be withdrawn via line 186 as a recycle stream. The cellulose ester wet cake in line 187 can have a total solids content of at least 1 weight percent, at least 50 weight percent, or at least 75 weight percent. Furthermore, the cellulose ester wet cake in line 187 can comprise cellulose ester in an amount of at least 70 weight percent, at least 80 weight percent, or at least 90 weight percent.

Once removed from separation zone 153, at least a portion of the cellulose ester solids from the cellulose ester wet cake can be washed in wash zone 154. Any methods known in the art suitable for washing a wet cake can be employed in wash zone 154. An exemplary washing technique suitable for use in the present invention includes, but is not limited to, a counter-current wash comprising at least 2 stages. In one embodiment, a wash liquid comprising a washing agent that is a non-solvent for cellulose ester can be introduced into wash zone 154 via line 188 to wash at least a portion of the cellulose ester solids. Such non-solvent washing agents include, but are not limited to, a C₁ to C₈ alcohol, water, or mixtures thereof. In one embodiment, the non-solvent washing agent can comprise methanol. In one embodiment, the wash liquid can additionally comprise water. Furthermore, as will be described in greater detail below, at least a portion of the wash liquid can optionally be introduced into wash zone 154 via line 194.

In one embodiment, washing of the cellulose ester solids in wash zone 154 can be performed in such a manner that at least a portion of any undesired byproducts and/or color bodies are removed from the cellulose ester solids. Byproducts and/or color bodies can be removed from the cellulose ester via the use of at least one bleaching agent in the wash liquid introduced via line 188. As used herein, the term “bleaching agent” shall denote any substance capable of decreasing the ΔE value of a cellulose ester, as defined below. When one or more bleaching agents are employed in wash zone 154, the wash liquid can contain the one or more bleaching agents in a total combined amount in the range of from about 0.001 to about 50 weight percent, or in the range of from 0.01 to 5 weight percent based on the total weight of the wash liquid.

In another embodiment, either in the alternative to or in addition to being contacted with a bleaching agent in wash zone 154, the cellulose ester can be contacted with a bleaching agent while still at least partially dissolved in ionic liquid (i.e., prior to being precipitated in precipitation zone 152). In this embodiment, the amount of bleaching agent employed can be in the range of from about 0.001 to about 2 weight percent, in the range of from about 0.002 to about 1 weight percent, or in the range of from 0.003 to 0.2 weight percent based on the entire weight of the cellulose ester-ionic liquid solution. Additionally, during contacting the bleaching agent employed in this embodiment can be introduced in the form of a dispersion in methanol at a concentration in the range of from about 0.00001 to about 50 weight percent, or in the range of from about 0.0001 to about 5 weight percent.

Examples of bleaching agents suitable for use in the present invention include, but are not limited to, chlorites, such as sodium chlorite (NaClO₂); hypohalites, such as sodium hypochlorite (NaOCl), sodium hypobromite (NaOBr), and the like; peroxides, such as hydrogen peroxide and the like; peracids, such as peracetic acid and the like; permanganates, such as potassium permanganate (KMnO₄) and the like; manganates; elemental metals, such as iron, manganese, copper, chromium, and the like; sodium sulfites, such as sodium sulfite (Na₂SO₃), sodium metabisulfite (Na₂S₂O₅), sodium bisulfite (NaHSO₃), and the like; perborates, such as sodium perborate (NaBO₃.nH₂O where n=1 or 4); chlorine dioxide (ClO₂); oxygen; and ozone. In one embodiment, the bleaching agent employed in the present invention can be selected from the group consisting of hydrogen peroxide, NaOCl, NaClO₂, and Na₂SO₃. In another embodiment, the bleaching agent employed in the present invention can comprise KMnO₄.

The resulting washed and/or bleached cellulose ester can have an a* value in the range of from about −5 to about 5, in the range of from about −2 to about 2, or in the range of from −1 to 1. Furthermore, the resulting washed and/or bleached cellulose ester can have a b* value in the range of from about −12 to about 12, in the range of from about −6 to about 6, or in the range of from −2 to 2. Additionally, the resulting washed and/or bleached cellulose ester can have an L* value of at least about 90, or at least 98. As used herein, the terms L*, a*, and b* respectively denote color values from black to white, red to green, and yellow to blue, and are determined according to the CIE 1976 color space as specified by the International Commission on Illumination.

In one embodiment, the resulting washed and/or bleached cellulose ester can have a ΔE value of less than 30, less than 15, or less than 5. Additionally, the washed and/or bleached cellulose ester can have a ΔE value that is at least 5, at least 10, or at least 20 percent lower than the ΔE value of the initial cellulose ester produced in esterification zone 140. As used herein, the term “ΔE” shall denote the color difference between a cellulose ester and the reference material n-methylpyrrolidone (“NMP”). By way of illustration, color measurements are taken for a sample of neat NMP followed by taking color measurements of a solution of cellulose ester dissolved in NMP. The ΔE value of the cellulose ester is then determined according to the following equation: ΔE=[(Δa*)²+(Δb*)²+(ΔL*)²]^(1/2) where Δa*, Δb*, and ΔL* are respectively the differences in a*, b* and L* values between the neat NMP and the solution of cellulose ester dissolved in NMP.

After washing in wash zone 154, a washed cellulose ester product can be withdrawn via line 189. The washed cellulose ester product in line 189 can be in the form of a wet cake, and can comprise solids in an amount of at least 1, at least 50, or at least 75 weight percent. Additionally, the washed cellulose ester product in line 189 can comprise cellulose ester in an amount of at least 1, at least 50, or at least 75 weight percent.

The washed cellulose ester product in line 189 can optionally be dried in drying zone 155. Drying zone 155 can employ any drying method known in the art to remove at least a portion of the liquid content of the washed cellulose ester product. Examples of drying equipment suitable for use in drying zone 155 include, but are not limited to, rotary dryers, screw-type dryers, paddle dryers, and/or jacketed dryers. In one embodiment, drying in drying zone 155 can be sufficient to produce a dried cellulose ester product comprising less than 5, less than 3, or less than 1 weight percent liquids.

After drying in drying zone 155, a final cellulose ester product can be withdrawn via line 190. The final cellulose ester product in line 190 can be substantially the same as the final cellulose ester product in line 90, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above at least a portion of the separated liquids generated in separation zone 153 can be withdrawn via line 186 as a recycle stream. The recycle stream in line 186 can comprise altered ionic liquid, one or more carboxylic acids, residual modifying agent, residual catalyst, residual acylating reagent, residual randomizing agent, and/or residual precipitation agent. Additionally, the recycle stream in line 186 can comprise one or more of the above-described co-solvents. As mentioned above, the term “altered ionic liquid” refers to an ionic liquid that has previously passed through a cellulose esterification step wherein at least a portion of the ionic liquid acted as an acyl group donor and/or recipient. As used herein, the term “modified ionic liquid” refers to an ionic liquid that has previously been contacted with another compound in an upstream process step. Therefore, altered ionic liquids are a subset of modified ionic liquids, where the upstream process step is cellulose esterification.

In one embodiment, the recycle stream in line 186 can comprise altered ionic liquid, one or more carboxylic acids, one or more alcohols, and/or water. In one embodiment, the recycle stream in line 186 can comprise altered ionic liquid in an amount in the range of from about 10 to about 99.99 weight percent, in the range of from about 50 to about 99 weight percent, or in the range of from 90 to 98 weight percent, based on the total weight of the recycle stream in line 186. In one embodiment, at least 50, at least 70, or at least 90 weight percent of the ionic liquid in the recycle stream in line 186 can ultimately be recycled for use in dissolving additional cellulose.

In one embodiment, the altered ionic liquid can comprise an ionic liquid having at least two different anions: primary anions and secondary anions. At least a portion of the primary anions in the altered ionic liquid can originate from the initial ionic liquid introduced into dissolution zone 120 via line 164, as described above. Additionally, at least a portion of the secondary anions in the altered ionic liquid can originate from the acylating reagent introduced into esterification zone 140, as described above. In one embodiment, the altered ionic liquid can comprise primary anions and secondary anions in a ratio in the range of from about 100:1 to about 1:100, in the range of from about 1:10 to about 10:1, or in the range of from 1:2 to 2:1. Additionally, the altered ionic liquid can comprise a plurality of cations, such as those described above with reference to the initial ionic liquid in line 68 of FIG. 1.

The recycle stream in line 186 can comprise a total amount of carboxylic acids in an amount in the range of from about 5 to about 60 weight percent, in the range of from about 10 to about 40 weight percent, or in the range of from 15 to 30 weight percent based on the total weight of ionic liquid in the recycle stream in line 186. Examples of suitable carboxylic acids the recycle stream in line 186 can comprise include, but are not limited to, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and isophthalic acid. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the carboxylic acids in the recycle stream in line 186 are acetic, propionic, and/or butyric acids.

Furthermore, the recycle stream in line 186 can comprise a total concentration of alcohols and/or water in an amount of at least 75 volume percent, at least 85 volume percent, or at least 95 volume percent, based on the total volume of the recycle stream. Examples of suitable alcohols the recycle stream in line 186 can comprise include, but are not limited to, C₁ to C₈ straight- or branched-chain alcohols. In one embodiment, at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the alcohol in the recycle stream in line 186 can comprise methanol.

As depicted in FIG. 2, at least a portion of the recycle stream in line 186 can be introduced into ionic liquid recovery/treatment zone 160. Ionic liquid recovery/treatment zone 160 can operate to segregate and/or reform at least a portion of the recycle stream from line 186. In one embodiment, at least a portion of the recycle stream can undergo at least one flash vaporization and/or distillation process to remove at least a portion of the volatile components in the recycle stream. At least 40 weight percent, at least 75 weight percent, or at least 95 weight percent of the volatile components in the recycle stream can be removed via flash vaporization. The volatile components removed from the recycle stream can comprise one or more alcohols. In one embodiment, the volatile components can comprise methanol. After vaporization, the resulting volatiles-depleted recycle stream can comprise a total amount of alcohols in the range of from about 0.1 to about 60 weight percent, in the range of from about 5 to about 55 weight percent, or in the range of from 15 to 50 weight percent.

In one embodiment, at least a portion of the carboxylic acids can be removed from the recycle stream. At least 10, at least 40, or at least 70 weight percent of the carboxylic acids present in said recycle stream can be removed. In one embodiment, this can be accomplished by first converting at least a portion of the carboxylic acids to carboxylate esters. In this embodiment, at least a portion of the recycle stream can be placed into a pressurized reactor where the recycle stream can be treated at a temperature, pressure, and time sufficient to convert the at least a portion of the carboxylic acid to alkyl esters (e.g., methyl esters), by reacting the carboxylic acids with alcohol present in the recycle stream. During esterification of the carboxylic acids, the pressurized reactor can have a temperature in the range of from about 100 to about 180° C., or in the range of from 130 to 160° C. Additionally, the pressure in the pressurized reactor during esterification can be in the range of from about 10 to about 1,000 pounds per square inch gauge (“psig”), or in the range of from 100 to 300 psig. The recycle stream can have a residence time in the pressurized reactor in the range of from about 10 to about 1,000 minutes, or in the range of from 120 to 600 minutes. Prior to the above-described esterification, the alcohol and carboxylic acid can be present in the recycle stream in a molar ratio in the range of from about 1:1 to about 30:1, in the range of from about 3:1 to about 20:1, or in the range of from 5:1 to 10:1 alcohol-to-carboxylic acid. In one embodiment, at least 5, at least 20, or at least 50 mole percent of the carboxylic acids can be esterified during the above-described esterification.

As mentioned above, at least a portion of the carboxylic acids can be acetic, propionic, and/or butyric acids. Additionally, as mentioned above, the alcohol present in the recycle stream can be methanol. Accordingly, the above-described esterification process can operate to produce methyl acetate, methyl propionate, and/or methyl butyrate. Subsequent to esterification, at least 10, at least 50, or at least 95 weight percent of the resulting carboxylate esters can be removed from the recycle stream by any methods known in the art. As depicted in FIG. 2, at least a portion of the carboxylate esters produced by the above described esterification can be routed to dissolution zone 120 and/or esterification zone 140 via line 196. Carboxylate esters introduced into dissolution zone 120 and/or esterification zone 140 can be employed as immiscible co-solvents, as described above. In another embodiment, at least a portion of the carboxylate esters can be converted to anhydrides via carbon monoxide insertion.

In one embodiment of the present invention, at least a portion of the altered ionic liquid present in the recycle stream can undergo reformation. Reformation of the altered ionic liquid can optionally be performed substantially simultaneously with the above-described esterification of the carboxylic acids in the recycle stream. Alternatively, reformation of the altered ionic liquid can be performed subsequently to the esterification of carboxylic acids in the recycle stream. Reformation of the altered ionic liquid can comprise at least one anion exchange process.

In one embodiment, reformation of the altered ionic liquid can comprise the step of anion homogenization via anion exchange, such that substantially all of the anions of the altered ionic liquid are converted to the same type of anion. In this embodiment, at least a portion of the altered ionic liquid can be contacted with at least one alkyl formate to assist in the anion exchange. Alkyl formates suitable for use in the present invention include, but are not limited to, methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, tert-butyl formate, hexyl formate, octyl formate, and the like. In one embodiment, the alkyl formate can comprise methyl formate. Additionally, reformation of the altered ionic liquid can be performed in the presence of one or more alcohols. Alcohols suitable for use in this embodiment of the invention include, but are not limited to, alkyl or aryl alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol and the like. In one embodiment, the alcohol present during reformation can comprise methanol.

The temperature during reformation of the altered ionic liquid can be in the range of from about 100 to about 200° C., or in the range of from 130 to 170° C. Additionally, the pressure during reformation of the altered ionic liquid can be at least 700 kPa, or at least 1,025 kPa. Furthermore, the reaction time of the reformation of the altered ionic liquid can be in the range of from about 10 min. to about 24 hours, or in the range of from 3 to 18 hours.

As mentioned above, reformation of the altered ionic liquid can comprise anion homogenization. In one embodiment, the resulting reformed ionic liquid can have an at least 90, at least 95, or at least 99 percent uniform anion content. Additionally, the reformed ionic liquid can comprise an alkyl amine formate. In one embodiment, the amine of the alkyl amine formate can be an imidazolium. Examples of alkyl amine formates suitable for use as the reformed ionic liquid include, but are not limited to, 1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazolium formate.

Following reformation, at least a portion of the volatile components in the reformed ionic liquid can optionally be removed via any methods known in the art for removing volatile components. Volatile components removed from the reformed ionic liquid can include, for example, carboxylate esters, such as those formed via the above described carboxylic acid esterification process. Thereafter, at least a portion of the reformed ionic liquid can undergo at least one anion exchange process to replace at least a portion of the anions of the reformed ionic liquid thereby forming a carboxylated ionic liquid. In one embodiment, the reformed ionic liquid can be contacted with at least one carboxylate anion donor to at least partially effect the anion exchange. Carboxylate anion donors suitable for use in this embodiment include, but are not limited to, one or more carboxylic acids, anhydrides, or alkyl carboxylates. Additionally, the carboxylate anion donors can comprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or aryl carboxylic acids, anhydrides, or methyl esters. Furthermore, the carboxylate anion donor can be one or more C₂ to C₁₂ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. Moreover, the carboxylate anion donor can be one or more C₂ to C₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters. The resulting carboxylated ionic liquid can comprise cations and anions substantially the same as those found in the carboxylated ionic liquid described above with reference to the carboxylated ionic liquid in line 64 of FIG. 1.

When contacting the reformed ionic liquid with one or more carboxylate anion donors, the contacting can be carried out in a contact mixture further comprising alcohol and/or water. In one embodiment, the alcohol and/or water can be present in the contact mixture in the range of from about 0.01 to about 20 molar equivalents per alkyl amine formate, or in the range of from 1 to 10 molar equivalents per alkyl amine formate. In one embodiment, methanol can be present in the contact mixture in the range of from 1 to 10 molar equivalents per alkyl amine formate.

Referring still to FIG. 2, in one embodiment, at least a portion of the carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can be part of a treated ionic liquid mixture further comprising at least one alcohol, one or more types of residual carboxylic acids, and/or water. The one or more alcohols and/or residual carboxylic acids found in the treated ionic liquid mixture can be substantially the same as described above with reference to the recycle stream in line 186. Following the above-described reformation process, the treated ionic liquid mixture can be subjected to at least one liquid/liquid separation process to remove at least a portion of the one or more alcohols in the mixture, if present. Such separation process can comprise any liquid/liquid separation process known in the art, such as, for example, flash vaporization and/or distillation. Additionally, the treated ionic liquid mixture can be subjected to at least one liquid/liquid separation process to remove at least a portion of the water, if present. Such separation process can comprise any liquid/liquid separation process known in the art, such as, for example, flash vaporization and/or distillation.

In one embodiment, at least 50, at least 70, or at least 85 weight percent of the alcohols and/or water can be removed from the treated ionic liquid mixture thereby producing a recycled carboxylated ionic liquid. At least a portion of the alcohol separated from the treated ionic liquid mixture can optionally be removed from ionic liquid recovery/treatment zone 160 via line 194. The one or more alcohols in line 194 can thereafter optionally be routed to various other points depicted in FIG. 2. In one embodiment, at least 50, at least 70, or at least 90 weight percent of the alcohols removed from the treated ionic liquid mixture can be routed to various other points in the process depicted in FIG. 2. In one optional embodiment, at least a portion of the alcohols in line 194 can be routed to randomization zone 151 to be employed as a randomizing agent. In another optional embodiment, at least a portion of the alcohols in line 194 can be routed to precipitation zone 152 to be employed as a precipitating agent. In yet another optional embodiment, at least a portion of the alcohols in line 194 can be routed to wash zone 154 to be employed as a wash liquid.

In one embodiment, at least a portion of the water separated from the treated ionic liquid mixture can optionally be removed from ionic liquid recovery/treatment zone 160 via line 192. Optionally, at least a portion of the water removed from ionic liquid recovery/treatment zone 160 can be routed to modification zone 110 to be employed as a modifying agent, as described above. At least about 5, at least about 20, or at least 50 weight percent of the water separated from the treated ionic liquid mixture can optionally be routed to modification zone 110. Additionally, at least a portion of the water in line 192 can optionally be routed to a waste water treatment process (not shown).

After alcohol and/or water removal, the above-mentioned recycled carboxylated ionic liquid can comprise residual carboxylic acid in an amount in the range of from about 0.01 to about 25 weight percent, in the range of from about 0.05 to about 15 weight percent, or in the range of from 0.1 to 5 weight percent based on the entire weight of the recycled carboxylated ionic liquid. Additionally, the recycled carboxylated ionic liquid can comprise sulfur in an amount of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw. Furthermore, the recycled carboxylated ionic liquid can comprise halides in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw. Moreover, the carboxylated ionic liquid can comprise transition metals in an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw.

In one embodiment, at least a portion of the recycled carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can optionally be routed to dissolution zone 120. At least 50 weight percent, at least 70 weight percent, or at least 90 weight percent of the recycled carboxylated ionic liquid produced in ionic liquid recovery/treatment zone 160 can be routed to dissolution zone 120.

In dissolution zone 120, the recycled carboxylated ionic liquid can be employed either individually or combined with the carboxylated ionic liquid entering dissolution zone 120 via line 164 to thereby form the above-described cellulose dissolving ionic liquid. In one embodiment, the recycled carboxylated ionic liquid can make up in the range of from about 10 to about 99.99 weight percent, in the range of from about 50 to about 99 weight percent, or in the range of from 90 to 98 weight percent of the cellulose dissolving ionic liquid in dissolution zone 120.

As mentioned above, in an alternative embodiment of the present invention, the cellulose dissolving ionic liquid employed can be a halide ionic liquid. When a halide ionic liquid is employed, the recycle stream in line 186 can have substantially the same composition as that described above, with the exception that a halide ionic liquid is present in place of the carboxylated ionic liquid. In this embodiment, removal of components such as volatiles (e.g., alcohols) and carboxylic acids can be performed in substantially the same manner as described above. The remaining halide ionic liquid can then be recycled to dissolution zone 120 without further processing (i.e., without an anion homogenization or anion exchange step). Concentrations of recycled halide ionic liquid in dissolution zone 120 can be the same as described above with reference to the recycled carboxylated ionic liquid.

This invention can be further illustrated by the following examples of embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLES Materials and Methods Used in Examples

Commercial grades of ionic liquids employed in the following examples were manufactured by BASF (Ludwigshafen, Germany) and were obtained through Fluka (a subsidiary of Sigma-Aldrich, St. Louis, Mo., USA). These ionic liquids were used either as received or after further purification as described in the examples that follow. Experimental ionic liquids (e.g., alkyl imidazolium carboxylates) were employed in the following examples, and were prepared as described in the examples that follow. Cellulose was obtained from Sigma-Aldrich (St. Louis, Mo., USA). The degree of polymerization (“DP”) of the Aldrich cellulose, which was approximately 335, was determined via capillary viscometry using copper ethylenediamine (Cuen) as the solvent. Prior to dissolution in ionic liquids, the cellulose was typically dried for 14-18 hours at 50° C. and a pressure of 5 mm Hg, except in cases where the cellulose was modified with water prior to dissolution.

Several of the Examples below indicate color values for various cellulose ester samples. All color measurements were made following the general protocol of ASTM D1925. Samples for color measurements were prepared by dissolving 1.7 g of cellulose ester in 41.1 g of n-methylpyrrolidone (“NMP”). A HunterLab Color Quest XE calorimeter with a 20 mm pathlength cell operating in transmittance mode was used for each of the measurements. The calorimeter was interfaced to a standard computer running EasyMatch QC Software (HunterLab). Color values (i.e., L*, white to black; a*, + red to − green; and b*, + yellow to − blue) were obtained for neat NMP and for the cellulose ester/NMP solutions. The color difference (ΔE) between the solvent and each of the sample solutions was then calculated in accordance with the definition for ΔE provided above.

Viscosity measurements provided in the following Examples were determined using an AR2000 rheometer (TA Instruments, LTD) interfaced with a computer running TA Instruments Advantage software. The 25 mm aluminum stage for the rheometer was enclosed in a plastic cover with a nitrogen purge to ensure that the samples did not acquire moisture during the measurements.

Example 1 Preparation of Cellulose Ester (Comparative)

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 61 g of 1-butyl-3-methylimidazolium chloride (“[BMIm]Cl”), which, prior to addition, had been melted at 90° C. and then stored in a desiccator where the [BMIm]Cl remained a liquid. While stirring rapidly, 3.21 g of previously dried microcrystalline cellulose, having a DP of about 335, was added in small portions over a period of 3 minutes. The slurry was stirred for 5 minutes and then placed under vacuum. After approximately 3 hours and 25 minutes, most of the cellulose had dissolved except for a few small pieces and 1 large piece attached to the probe. After 5.5 hours, the oil bath temperature was increased to 105° C. to speed up dissolution of the remaining cellulose. The solution was maintained at 105° C. for 1.5 hours (47 minute heat up) before allowing the solution to cool to room temperature and stand overnight at ambient temperature.

After standing overnight, the cellulose-[BMIm]Cl solution was clear and the IR spectra indicated that all of the cellulose was dissolved. After heating the solution to 80° C., 10.11 g (5 equivalents) of acetic anhydride (“Ac₂O”) was added dropwise over a period of 26 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of methanol (“MeOH”). The solid from each aliquot was washed twice with 100 mL portions of MeOH then twice with 100 mL of MeOH containing 8 weight percent of 35% H₂O₂ before drying at 60° C. and 5 mm Hg. The first sample was white, the second sample was tan, and the third sample was brown. During the course of the reaction, the solution became progressively darker. Approximately 2 hours and 45 minutes after the start of the Ac₂O addition, the viscosity of the reaction mixture abruptly increased, and then the reaction mixture completely gelled. The oil bath was lowered and the contact solution was allowed to cool to room temperature.

FIG. 3 is a plot of absorbance versus time for Example 1 and it shows the dissolution of cellulose (1,046 cm⁻¹) and the removal of residual water (1,635 cm⁻¹) from the mixture during the course of the dissolution. The spikes in the cellulose trend line are due to large cellulose gel particles, which are removed by the stirring action, sticking to the IR probe. Clumping occurs because the surfaces of the cellulose particles become partially dissolved before dispersion is obtained, which can lead to clumping and large gel particles. The dip in the trend lines near the 6 hour mark is a result of the temperature increase from 80 to 105° C. This figure illustrates that approximately 6 hours is required to fully dissolve the cellulose when the cellulose is added to the ionic liquid that is preheated to 80° C.

FIG. 4 is a plot of absorbance versus time for Example 1 and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The degree of substitution (“DS”) values shown in FIG. 4 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. As illustrated, approximately 75% of the acetylation occurred during the first hour, after which the reaction rates slowed. Approximately 2 hours and 45 minutes from beginning the Ac₂O addition (DS=2.45), the solution viscosity suddenly increased followed by gelation of the contact mixture. At this point, no further reaction occurred and the remaining contact solution was processed as described above. It should be noted that there was still a large excess of Ac₂O at the point of gelation. Furthermore, during the course of the contact period, the solution became progressively darker and the final product color was dark brown. Color measurements of the final sample dissolved in NMP gave an L* value of 82.74, an a* value of 2.23, a b* value of 56.94, and an ΔE value of 59.55. In addition to determining the DS of each sample, the molecular weight of each sample was determined by gel permeation chromatography (“GPC”) (reproduced in Table 2, below). In general, the weight average molecular weight (“Mw”) was approximately 55,000 and the polydispersity ranged from 3-4. Based on the DP of the starting cellulose, this analysis indicates that the molecular weight of the cellulose polymer remained essentially intact during the contact period.

Example 2 Modification of Cellulose with Water

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 64.3 g of [BMIm]Cl, which, prior to addition, had been melted at 90° C. and then stored in a desiccator where the [BMIm]Cl remained a liquid. While stirring rapidly, 3.4 g (5 weight percent) of microcrystalline cellulose, having a DP of about 335, was added at ambient temperature. Approximately 12 minutes after adding the cellulose, the flask was placed in a preheated 80° C. oil bath. After about 17 minutes in the 80° C. oil bath, upon visual inspection all of the cellulose appeared to be dissolved. A vacuum was applied after approximately 22 minutes in the 80° C. oil bath. To insure complete removal of water, 50 minutes after applying vacuum, the oil bath setting was increased to 105° C. and the solution was stirred for 2 hours and 25 minutes before the oil bath was allowed to cool to room temperature.

The temperature of the clear, amber cellulose solution was adjusted to 80° C. before adding 6.42 g of Ac₂O (3 eq.) dropwise over a period of 5 minutes. The contact mixture was sampled throughout the reaction period by removing 6 to 10 g aliquots of the contact mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed once with 100 mL of MeOH then twice with MeOH containing 8 weight percent of 35% H₂O₂. The samples were then dried at 60° C. at a pressure of 5 mm Hg overnight. During the course of the contact period the color of the solution became darker, ultimately becoming dark brown. Approximately 2 hours and 10 minutes from the start of Ac₂O addition, the solution viscosity began to increase significantly; 10 minutes later the solution completely gelled and started climbing the stir shaft. The experiment was aborted and MeOH was added to the flask to precipitate the remaining product.

The precipitation and the wash liquids from each aliquot were combined and concentrated in vacuo at 68° C. until the vacuum dropped to 24 mm Hg, which provided 54.2 g of recovered [BMIm]Cl. Analysis by ¹H NMR revealed that the ionic liquid contained 4.8 weight percent acetic acid when measured by this technique.

FIG. 5 is a plot of absorbance versus time for Example 2, and it shows the dissolution of cellulose (1,046 cm⁻¹) and the removal of residual water (1,635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen in FIG. 5, the dissolution of the cellulose was very rapid (17 minutes, compared to 360 minutes in Example 1). This was due to adding the cellulose to the ionic liquid at room temperature, stirring to get a good dispersion (higher surface area), then heating to effect dissolution. Normally, [BMIm]Cl is a solid at room temperature, and melts at approximately 70° C. However, if water or a carboxylic acid is allowed to mix with [BMIm]Cl, the [BMIm]Cl will remain a liquid at room temperature, thus allowing introduction of the cellulose at ambient temperature. As can be seen from the water loss in FIG. 5, the [BMIm]Cl contained a significant amount water. This example illustrates that the addition of water to an ionic liquid followed by cellulose addition and good mixing to get a good dispersion allows for rapid dissolution of cellulose.

FIG. 6 is a plot of absorbance versus time for Example 2, and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 6 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Relative to Example 1, the reaction rate was slower (Example 1 indicates a DS of 2.44 at 165 minutes, whereas Example 2 indicates a DS of only 2.01 at 166 minutes; compare Table 2, below). Similar to what was observed in Example 1, the solution viscosity suddenly increased followed by gelation of the contact mixture, but in Example 2, gelation occurred at a lower DS. Both the slower reaction rate and gelation at a lower temperature can be attributed to the use of less Ac₂O. However, it should be noted that there was still a large excess of Ac₂O at the point of gelation. As with Example 1, during the course of the contact period, the solution became progressively darker and the final product color was dark brown. Color measurements of the final sample dissolved in NMP gave an L* value of 67.30, an a* value of 17.53, a b* value of 73.35, and a ΔE value of 82.22. In addition to determining the DS of each sample, the molecular weight of each sample was determined by GPC (Table 2, below). In general, Mw was approximately 55,000 and the polydispersity ranged from 3-6. Based on the DP of the starting cellulose, this analysis indicates that the molecular weight of the cellulose polymer remained essentially intact during the contact period.

Example 3 MSA Secondary Component, No Modification with Water

3.58 g of cellulose (5 weight percent) was dissolved in 68 g of [BMIm]Cl in a manner similar to Example 2. At a temperature of 80° C., a mixture of 433 mg (0.2 eq.) of methane sulfonic acid (“MSA”) and 6.76 g of Ac₂O (3 eq.) was added to the cellulose solution dropwise over a period of 8 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed twice with 100 mL portions of MeOH then dried at 60° C. at a pressure of 5 mm Hg. The solid samples were snow white. After approximately 2 hours, all of the Ac₂O appeared to be consumed, according to the IR spectrum. The experiment was aborted and the remaining sample was processed as above.

The precipitation and the wash liquids from each aliquot were combined and concentrated in vacuo at 68° C. until the vacuum dropped to 24 mm Hg, which provided 64 g of recovered [BMIm]Cl. Unlike Example 2, analysis by ¹H NMR revealed that the ionic liquid did not contain any acetic acid when measured by this technique. This result indicates that MSA aids in the removal of residual acetic acid from the ionic liquid, probably by conversion of the residual acetic acid to methyl acetate.

FIG. 7 is a plot of absorbance versus time for Example 3, and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 7 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. What is apparent from FIG. 7 is that the rates of reaction are much faster compared to Examples 2 and 3. For example, 55 minutes were required to reach a DS of 1.82 in Example 1-1 (Table 2, below) while only 10 minutes were required to reach a DS of 1.81 in Example 3-1. Similarly, 166 minutes were required to reach a DS of 2.01 in Example 2-4 (Table 2, below) while only 20 minutes were required to reach a DS of 2.18 in Example 3-2. Additionally, FIG. 7 shows that no gelation occurred during the course of the experiment. In fact, throughout the experiment, there was no increase in solution viscosity, the solution color was essentially unchanged from the initial solution color, and the products isolated from the contact mixture were all white. Color measurements of the final sample dissolved in NMP gave an L* value of 97.65, an a* value of −2.24, a b* value of 11.07, and a ΔE value of 11.54. Comparison of these values to those obtained in Examples 1 and 2 (ΔE=59.55 and 82.22, respectively) shows that inclusion of a secondary component such as MSA in the contact mixture significantly improves solution and product color. This effect is particularly pronounced in view of the fact that the samples in Examples 1 and 2 were bleached and the samples in this Example were not bleached. As discussed in Example 36, below, bleaching can significantly improve product color for cellulose esters prepared from cellulose dissolved in ionic liquids. Finally, it should be noted in Table 2, below, that the Mw (ca. 40,000) for the samples of Example 3 are less than those for Examples 1 and 2, and that the polydispersity (Mw/Mn) is lower and more narrow (2-3) than those for Examples 1 and 2 (3-6). When compared to Examples 1 and 2, Example 3 shows that inclusion of a secondary component, such as MSA, in the contact mixture accelerates the rates of reaction, significantly improves solution and product color, prevents gelation of the contact mixture, allows the achievement of high DS values while using less acylating reagent, and helps to promote lowering of the cellulose ester molecular weight.

TABLE 2 Properties of Cellulose Acetates Prepared in Examples 1 through 3 Example Time (min) DS Mw Mw/Mn 1-1 55 1.82 59243 3.29 1-2 122 2.25 61948 4.34 1-3 165 2.44 51623 3.73 2-1 6 0.64 50225 2.93 2-2 34 1.49 56719 3.48 2-3 56 1.73 64553 5.4 2-4 166 2.01 66985 5.7 2-5 176 2.05 63783 5.83 3-1 10 1.81 41778 1.92 3-2 20 2.18 43372 2.01 3-3 27 2.39 41039 2.22 3-4 43 2.52 41483 2.4 3-5 66 2.62 40412 2.54 3-6 124 2.72 39521 2.55

Example 4 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 58.07 g of [BMIm]Cl, which, prior to addition, had been melted at 90° C. and then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C.

3.06 g of water was added to 3.06 g (5 weight percent) of microcrystalline cellulose having a DP of approximately 335. The slurry was hand mixed and allowed to stand for approximately 30 minutes before adding the slurry in small portions to the [BMIm]Cl over a period of 5 minutes. This gave a hazy solution in which the cellulose was surprisingly well dispersed. The slurry was stirred for 27 minutes and then placed under vacuum. After 28 minutes under vacuum, it appeared upon visual inspection that all of the cellulose had dissolved. Dissolution of the cellulose was confirmed by IR. According to the IR analysis, there was still approximately 3 weight percent water in the [BMIm]Cl after all of the cellulose was dissolved. The system was maintained under vacuum at 80° C. to remove the remaining water. The sample was then allowed to cool to room temperature and left standing until the next step.

After heating the cellulose solution to 80° C., a mixture of 5.78 g Ac₂O (3 eq.) and 368 mg MSA (0.2 eq.) was added dropwise over a period of 8 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed twice with 100 mL portions of MeOH then dried at 60° C. at a pressure of 5 mm Hg. The isolated samples were all white. The solution color was excellent throughout the experiment and there was no indication of a viscosity increase. After approximately 2 hours and 25 minutes, infrared spectroscopy indicated that all of the Ac₂O was consumed. The experiment was aborted and the remaining sample was processed as above.

FIG. 8 is a plot of absorbance versus time for Example 4, and it shows the dissolution of cellulose (1,046 cm⁻¹) and the removal of residual water (1,635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water-wet (activated) cellulose was very rapid (28 minutes) despite the presence of a significant amount of water. This is surprising in view of the conventional teachings. The addition of water-wet cellulose to the ionic liquid enables one to obtain a good dispersion of cellulose with little clumping. Upon application of a vacuum to remove the water, the cellulose rapidly dissolves without clumping to form large particles.

FIG. 9 is a plot of absorbance versus time for Example 4, and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 9 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Relative to Example 3, the reaction rate to produce cellulose acetate was similar. However, the weight average molecular weights of the cellulose acetate prepared in Example 4 (approximately 33,000; see Table 3, below) were notably lower than those observed in Example 3 and much lower than those observed in Examples 1 and 2 (see Table 2, above). Additionally, the polydispersities for the samples of Example 4 are all less than 2, which are less than those observed for the samples produced in Examples 1, 2, and 3.

This example illustrates that water-wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution. The reaction rate for formation of cellulose acetate is rapid. Surprisingly, the use of water-wet cellulose leads to lower molecular weight cellulose acetate with low polydispersities relative to the use of dry cellulose. Additionally, the cellulose acetate made from water-wet cellulose has better acetone solubility relative to when dry cellulose is utilized.

Example 5 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 67.33 g of [BMIm]Cl, which, prior to addition, had been melted at 90° C. and then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. 7.08 g of water was added to 7.48 g (10 weight percent) of microcrystalline cellulose, which had a DP of approximately 335. The cellulose slurry was hand mixed and allowed to stand for about 60 minutes before adding the slurry in small portions to the [BMIm]Cl over a period of 8 minutes. This produced a hazy solution in which the cellulose was surprisingly well dispersed. The slurry was stirred for 10 minutes and then placed under vacuum. The cellulose dispersion was then stirred overnight.

Infrared spectroscopy indicated that essentially all of the cellulose was dissolved within 50 minutes after applying vacuum; approximately 3.5 hours were required to remove the water. A mixture of 14.13 g of Ac₂O (3 eq.) and 884 mg (0.2 eq.) of MSA was added to the cellulose solution dropwise over a period of 11 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed twice with 100 mL portions of MeOH then dried at 60° C. and a pressure of 5 mm Hg. The isolated samples were snow white. The solution color was excellent throughout the experiment and there was no indication of a viscosity increase. After approximately 2 hours and 10 minutes, infrared spectroscopy indicated that all of the Ac₂O was consumed. The experiment was aborted and the remaining sample was processed as above.

FIG. 10 is a plot of absorbance versus time for Example 5 and it shows the dissolution of cellulose (1,046 cm⁻¹) and the removal of residual water (1,635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water-wet (activated) cellulose was very rapid (50 minutes) despite the presence of a significant amount of water and the increase in cellulose concentration relative to Example 4.

FIG. 11 is a plot of absorbance versus time for Example 5 and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 11 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Despite the increase in cellulose concentration, relative to Examples 3 and 4, the reaction rate to produce cellulose acetate in Example 5 was similar. The weight average molecular weights of the cellulose acetate prepared in Example 5 (approximately 22,000; see Table 3, below) were notably lower than those observed in Example 4 and much lower than those observed in Examples 1, 2, and 3 (see Table 2, above). As was observed for Example 4, the polydispersities for the samples of Example 5 are all less than 2, which are less than those observed for the samples produced in Examples 1, 2, and 3.

This example illustrates that water-wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution even when the cellulose concentration is increased to 10 weight percent. The reaction rate for formation of cellulose acetate is rapid. Surprisingly, the use of water-wet cellulose at these concentrations leads to even lower molecular weight cellulose acetates with low polydispersities relative to the use of dry cellulose. The cellulose acetate made from water-wet cellulose has better acetone solubility relative to when dry cellulose is utilized.

Example 6 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 51.82 g of [BMIm]Cl, which, prior to addition, had been melted at 90° C. and then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. 53.6 g of water was added to 9.15 g (15 weight percent) of microcrystalline cellulose, which had a DP of approximately 335. The cellulose slurry was hand mixed and allowed to stand in the water for 50 minutes before filtering, which produced 18.9 g of a wet cellulose cake. The water-wet cellulose was then added in small portions to the [BMIm]Cl over a period of 5 minutes. Within 2 minutes, the cellulose was finely dispersed in the ionic liquid. Ten minutes after adding the cellulose to the [BMIm]Cl, the flask was placed under vacuum. After about 1 hour, there were no visible cellulose particles; the solution viscosity was very high and the solution started climbing the stir rod. The solution was left stirring overnight at 80° C. under vacuum.

Infrared spectroscopy indicated that about 1 hour was required for cellulose dissolution and 2 hours were required to strip the water to the initial value. The cellulose solution was heated to 100° C., followed by addition of a mixture of 17.28 g Ac₂O (3 eq.) and 1.087 g (0.2 eq.) of MSA, added dropwise over a period of 8 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed once with 100 mL of MeOH then twice with MeOH containing 8 weight percent of 35% H₂O₂. The solid samples were then dried at 60° C. at a pressure of 5 mm Hg. After about 65 minutes, infrared spectroscopy indicated that all of the Ac₂O was consumed. The experiment was aborted and the remaining sample was processed as above.

FIG. 12 is a plot of absorbance versus time for Example 6, and it shows the dissolution of presoaked water-wet cellulose (1,046 cm⁻¹) and the removal of residual water (1,635 cm⁻¹) from the mixture during the course of the dissolution. As can be seen, the dissolution of the water-wet (activated) cellulose was very rapid (60 minutes), despite the presence of a significant amount of water and the use of 15 weight percent cellulose. Even more surprising was the rapid removal of water (about 2 hours) at this high cellulose concentration.

FIG. 13 is a plot of absorbance versus time for Example 6, and it illustrates the acetylation of cellulose (1,756; 1,741; 1,233 cm⁻¹), the consumption of Ac₂O (1,822 cm⁻¹), and the coproduction of acetic acid (1,706 cm⁻¹) during the experiment. The DS values shown in FIG. 13 were determined by NMR spectroscopy and correspond to the samples removed during the course of the contact period. Despite the increase in cellulose concentration (15 weight percent), acetic anhydride could be easily mixed into the cellulose solution at 100° C. Again, the weight average molecular weights of the cellulose acetate prepared in Example 6 (approximately 20,000; see Table 3, below) were notably lower than those observed in Examples 1, 2, and 3 (approximately 39,000 to 67,000; see Table 2, above) where the cellulose was dried prior to use. Also, the polydispersities for the samples of Example 6 are all less than 2, which are less than those observed for the samples produced in Examples 1, 2, and 3.

This example illustrates that water-wet cellulose leads to good cellulose dispersion in the ionic liquid and rapid cellulose dissolution even when the cellulose concentration is increased to 15 weight percent. This example also shows that higher temperatures (e.g., 100° C.) can increase reaction rates for formation of cellulose acetate. Surprisingly, the use of water-wet cellulose at these concentrations leads to even lower molecular weight cellulose acetates with low polydispersities compared to the use of an initially dry cellulose. Furthermore, the cellulose acetate made from water-wet cellulose has better acetone solubility relative to when initially dry cellulose is utilized.

TABLE 3 Effect of Water Modification on Properties of Cellulose Acetates Example Time (min) DS Mw Mw/Mn 4-1 9 1.58 31732 1.73 4-2 13 1.94 33559 1.64 4-3 21 2.15 34933 1.63 4-4 35 2.28 31810 1.77 4-5 150 2.63 30771 1.89 5-1 11 1.95 24522 1.6 5-2 14 2.21 23250 1.67 5-3 18 2.35 22706 1.76 5-4 22 2.52 22692 1.79 5-5 31 2.59 21918 1.86 5-6 45 2.60 21628 1.89 5-7 70 2.66 19708 1.97 5-8 130 2.67 20717 1.99 6-1 10 2.63 20729 1.67 6-2 14 2.75 19456 1.78 6-3 18 2.80 19658 1.84 6-4 23 2.87 18966 1.84 6-5 32 2.89 20024 1.88 6-6 65 2.96 18962 1.85

Example 7 Miscible Co-Solvent

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 58.79 g of [BMIm]Cl, which, prior to addition, had been melted at 90° C. and then stored in a desiccator. The flask was placed in an oil bath and heated to 80° C. After reaching 80° C., IR spectra data gathering was initiated before adding 1.82 g (3 weight percent) of glacial acetic acid. The mixture was stirred for 12 minutes before adding 10.38 g (15 weight percent) cellulose (having a DP of approximately 335) as a water-wet cellulose cake (10.29 g water, prepared by soaking the cellulose for 50 minutes in excess water) over a period of 9 minutes. The mixture was then stirred for approximately 9 minutes to allow the cellulose to disperse before applying a vacuum. After about 65 minutes, infrared spectroscopy indicated that all of the cellulose was dissolved (see FIG. 14). The solution was stirred for an additional 70 minutes before adding 1.82 g of glacial acetic acid (6 weight percent total). In order to reduce the solution viscosity, the stirring was turned off 8 minutes after adding the acetic acid and the oil bath temperature was increased to 100° C. After reaching 100° C., stirring was resumed. Infrared spectroscopy indicated that upon resumed stirring, the acetic acid mixed well with the cellulose solution. The final solution was clear and no cellulose particles were observed. After standing for 10 days, the cellulose solution was still clear and could be hand stirred at room temperature.

This example shows that a significant amount of a miscible co-solvent that is compatible with cellulose acylation, such as a carboxylic acid (e.g., acetic acid), can be mixed with a cellulose-ionic liquid sample while still maintaining cellulose solubility. The use of such a co-solvent apparently has the unexpected benefit of reducing solution viscosity, allowing for easier processing.

Example 8 Randomization

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 149.7 g of [BMIm]Cl. The flask was placed in an oil bath and heated to 80° C. 12.14 g of microcrystalline cellulose (7.5 weight percent; having a DP of approximately 335) was added to 68.9 g of water. After hand mixing, the cellulose was allowed to stand in the water for 45 minutes at 60° C. before filtering, which yielded 24.33 g of a wet cellulose cake. The water-wet cellulose was then added in small portions to the [BMIm]Cl over a period of 5 minutes. Approximately 15 minutes after adding the cellulose to the [BMIm]Cl, the flask was placed under vacuum by gradually lowering the vacuum, starting at about 120 mm Hg and ending at about 1.4 mm Hg. After approximately 85 minutes, no visible cellulose particles remained in the mixture and analysis by infrared spectroscopy indicated that all of the cellulose was dissolved. The solution was stirred overnight at 80° C. under vacuum.

After heating the cellulose solution to 80° C., a mixture of 22.93 g Ac₂O (3 eq.) and 1.427 g (0.2 eq.) of MSA was added dropwise over a period of 15 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed three times with 100 mL portions of MeOH then dried at 60° C. at a pressure of 5 mm Hg. After removing an aliquot 192 minutes after the start of the Ac₂O addition, 1.21 g of MeOH was added to the contact mixture. The contact mixture was stirred for an additional 120 minutes before adding 1.95 g of water. The contact mixture was then stirred overnight at 80° C. (14 hours and 40 minutes) at which time, the experiment was aborted and the remaining sample was processed as above.

The contact times, DS, and molecular weights for isolated samples removed from the contact mixture prepared above are summarized below in Table 4.

TABLE 4 Effect of Randomization on Cellulose Acetates Example Time (min) DS Mw Mw/Mn 8-1 16 1.95 26492 1.54 8-2 18 2.15 24838 1.57 8-3 21 2.24 23973 1.63 8-4 25 2.33 23043 1.7 8-5 32 2.42 23499 1.79 8-6 57 2.56 21736 1.82 8-7 190 2.73 20452 2.08 8-8 After MeOH Addition 2.73 20478 2.00  8-10 After H₂O Addition 2.59 21005 1.89

As indicated in Table 4, as contact time increased, the DS of the cellulose acetate increased (until water was added) and the Mw decreased. Fifty-seven minutes after starting the contact period, the cellulose acetate sample had a DS of 2.56 and a Mw of 21,736. Prior to adding the MeOH/water, the DS was 2.73 and the Mw was 20,452. After the water contact period, the isolated cellulose acetate had a DS of 2.59 and a Mw of 21,005 indicating that the DS was reduced but the Mw was unchanged.

FIG. 15 shows the proton NMR spectra of a cellulose acetate prepared by direct acetylation (DS=2.56) and after randomization (DS=2.59). Both the ring protons attached to the anhydroglucose monomers and acetyl protons attached to the acetyl substituents are shown. FIG. 15 demonstrates that even though these two cellulose acetates have essentially the same DS, they have a much different monomer content.

Example 9 MSA Secondary Component, Minimal Acylating Reagent

A 3-neck 100 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 60.47 g of 1-allyl-3-methylimidazolium chloride (“[AMIm]Cl”). The flask was placed in an oil bath and heated to 80° C. 9.15 g of microcrystalline cellulose (13 weight percent; having a DP of approximately 335) was added to 27.3 g of water. After hand mixing, the cellulose was allowed to stand in the water for 50 minutes at 60° C. before filtering, which yielded 9.44 g of a wet cellulose cake. The water-wet cellulose was then added in small portions to the [AMIm]Cl over a period of 5 minutes. Approximately 15 minutes after adding the cellulose to the [AMIm]Cl, the flask was placed under vacuum by gradually lowering the pressure, starting at about 120 mm Hg. After approximately 40 minutes, no visible cellulose particles remained in the mixture and analysis by infrared spectroscopy indicated that all of the cellulose was dissolved. The solution was left stirring overnight at 80° C. under vacuum.

After heating the cellulose solution to 80° C., a mixture of 8.58 g Ac₂O (3 eq.) and 537 mg (0.2 eq.) of MSA was added dropwise over a period of 5 minutes. The reaction was sampled throughout the reaction period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed three times with 100 mL portions of MeOH and then dried at 60° C., 5 mm Hg. After all of the Ac₂O appeared to be consumed according to infrared spectroscopy, the experiment was aborted and the remaining sample was processed as above.

The contact times, DS and molecular weights for isolated samples removed from the contact mixture prepared above are summarized below in Table 5.

TABLE 5 Contact Times and Properties of Cellulose Acetate Prepared in [AMIm]Cl. Example Time (min) DS Mw Mw/Mn 9-1 5 1.74 36192 1.69 9-2 8 2.24 35734 1.84 9-3 11 2.38 32913 1.9 9-4 15 2.48 31811 1.99 9-5 24 2.60 31970 2.14 9-6 50 2.74 31302 2.36 9-7 109 2.82 30808 2.48

As indicated in Table 5, five minutes after starting the reaction the first cellulose acetate sample had a DS of 1.74 and a Mw of 36,192. With increasing contact time, the DS increased and the Mw decreased. After 109 minutes, the DS was 2.82 and the Mw was 30,808. This example shows that, compared to conventional methods, the method of Example 9 provides for a higher DS and a significant reduction in cellulose acetate molecular weight. By way of comparison, the conventional method described in Example 11, which is discussed in further detail below, requires 6.5 hours to yield a cellulose acetate with a DS of 2.42 and a Mw of 50,839, while in Example 9, a cellulose acetate with a DS of 2.48 and a Mw of 31,811 was achieved in only 15 minutes.

Example 10 Conventional Cellulose Ester Preparation (Comparative)

A solution of cellulose (5 weight percent) dissolved in 29.17 g of [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (approximately 7 mm Hg) while stirring for 2 hours. To the cellulose solution was added 4.6 g (5 eq.) of Ac₂O over a period of 5 minutes. During the course of the reaction, the solution color became gradually darker (brown). After 2.5 hours, the solution had gelled, so the contact solution was allowed to cool to room temperature. The product was isolated by adding the solution to water then homogenizing to give a dispersed gel/powder. The mixture was filtered and washed extensively with water. After drying the solid in vacuo at 50° C., 2.04 g of a pink powder was obtained that was insoluble in acetone. Analysis by ¹H NMR indicated that the sample had a DS of 2.52 and a Mw of 73,261.

Example 11 Conventional Cellulose Ester Preparation (Comparative)

33.8 g of [AMIm]Cl was added to a 3-neck 100 mL round bottom flask equipped for mechanical stirring and having an N₂/vacuum inlet added. While stirring rapidly, 1.78 g of dry cellulose powder (5 weight percent; having a DP of approximately 335) was added to the [AMIm]Cl. The flask was then placed under vacuum (2 mm Hg) and the mixture was stirred at room temperature to insure that the cellulose was well dispersed. After 15 minutes, the cellulose was well dispersed and the solution viscosity was rising. The flask was then placed in an oil bath which was heated to 80° C. After 40 minutes, all of the cellulose was dissolved. The solution was maintained at 80° C. for 6.5 hours before allowing the solution to cool to room temperature and stand overnight.

The viscous solution was heated to 80° C. before adding 5.6 g (5 eq.) of Ac₂O dropwise over a period of 15 minutes. After 5 hours, the product was isolated by pouring the mixture into 300 mL of MeOH. The MeOH/solid slurry was stirred for approximately 30 minutes before filtering to remove the liquids. The solid was then taken up in two 200 mL portions of MeOH and the slurry was stirred for approximately 30 minutes before filtering to remove the liquids. The solids were dried overnight at 55° C. and a pressure of 6 mm Hg, yielding 2.27 g of a powder, which, when dissolved in acetone, gave a hazy acetone solution. Analysis by ¹H NMR and by GPC indicated that the sample had a DS of 2.42 and a Mw of 50,839.

Example 12 MSA Secondary Component, Long Chain Aliphatic Cellulose Esters

A solution of cellulose (5 weight percent) dissolved in [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (approximately 2.5 mm Hg) while stirring for 4 hours. A mixture of 10.88 g (5 eq.) of nonanoic anhydride and 141 mg of MSA was added to the cellulose solution over a period of 25 minutes. After 18.5 hours, the solution was allowed to cool to room temperature before it was poured into a solution of 80:20 MeOH:H₂O. After filtering, the solid was washed extensively with 85:15 MeOH:H₂O, followed by washing with 95:5 MeOH:H₂O. The sample was dried in vacuo which gave 3.7 g of a white powder soluble in isododecane. Analysis by ¹H NMR indicated that the resulting product was cellulose nonanoate having a DS of 2.49.

Achievement of a cellulose nonanoate with a high degree of substitution by the method of this example is surprising in view of conventional teachings that long chain aliphatic cellulose esters with a DS greater than about 1.5 cannot be prepared in ionic liquids.

Example 13 MSA Secondary Component, C₃ and C₄ Aliphatic Cellulose Esters

A solution of cellulose (5 weight percent) dissolved in [BMIm]Cl was heated to 80° C. with an oil bath. The solution was held under vacuum (approximately 6 mm Hg) while stirring overnight. A mixture of 7.91 g (5 eq.) of butyric anhydride and 190 mg of MSA was added to the cellulose solution over a period of 25 minutes. After 2.6 hours, the solution was allowed to cool to room temperature before it was poured into water. The solid was washed extensively with water before drying in vacuo, which yielded 2.62 g of a white powder soluble in acetone and 90:10 CHCl₃:MeOH. Analysis by ¹H NMR indicated that the resulting product was cellulose butyrate having a DS of 2.59.

This example illustrates that C₃ and C₄ aliphatic cellulose esters having high degrees of substitution can be prepared by the methods of this example.

Example 14 Homogenization of Cellulose Solution

193.6 g of solid [BMIm]Cl was added to a 1 L flat bottom kettle. A 3 neck top was placed on the kettle and the kettle was fitted with an N₂/vacuum inlet and for mechanical stirring. The kettle was then placed in an 80° C. oil bath and the [BMIm]Cl was melted while stirring under a vacuum of 6 mm Hg. After the [BMIm]Cl was completely melted, 10.2 g of previously dried cellulose (having a DP of about 335) was added and the mixture and was thereafter homogenized with a Heidolph Silent Crusher. After about 3 minutes of homogenization, essentially all of the cellulose was dissolved. The resulting solution was then stirred under vacuum (6 mm Hg) for an additional 1.5 hours, at which time all of the cellulose was dissolved.

This example illustrates that high intensity mixing can be used to disperse the cellulose which leads to rapid cellulose dissolution. This result may be due to the increased surface area of the cellulose resulting from mixing.

Example 15 Acetone Solubility

The solubilities of cellulose acetate in acetone were evaluated as follows: Acetone (Burdick & Jackson, high purity grade) was dried using 4A molecular sieves (purchased from Aldrich and stored in an oven at 125° C.). All of the cellulose acetate samples were dried prior to use in a Eurotherm 91e vacuum oven (manufactured by Eurotherm Inc., Leesburg, Va., USA) at 60° C. and a pressure of 5 mm Hg for at least 12 hours. Each cellulose acetate sample was weighed into a 2 Dram vial (100 mg±1 mg; obtained from VWR); thereafter, 1 mL±5 μL of dry acetone was added to each of the vials. The vials were then placed in an ultrasonic bath (VWR, model 75HT) and ultra-sonicated at room temperature for 30-120 minutes, then removed and vortexed (VWR minivortexer) at room temperature using a speed setting of 10. If the cellulose acetate appeared to be dissolving but the rate of dissolution appeared to be slow, the vial was placed on a roller and mixed at approximately 15 revolutions per minute overnight at ambient temperature. Following the mixing period, the solubility of each cellulose acetate was rated as follows:

Rating Description 1 Soluble, transparent with no visible particles 2 Partially soluble, hazy 3 Partially soluble, very hazy, visible particles 4 Gel 5 Swollen solid 6 Insoluble Cellulose acetates with a rating of 1 are very useful in all applications in which acetone solubility or solubility in related solvents (e.g., diethyl phthalate) is a critical factor (e.g., solvent spinning of acetate fiber or melt processing of plasticized cellulose acetate). Cellulose acetates with a rating of 2 or 3 would require additional filtration to remove insoluble particles and/or the use of co-solvents before they would have utility. Cellulose acetates with a rating of 4-6 would not have utility in these applications. Hence, cellulose acetates with a rating of 1 are highly desired.

In Table 6, the solubility in acetone of cellulose acetates prepared in Examples 3-6, 8, and 9 are compared to the solubilities of the cellulose acetates prepared in Examples 1 and 2, and to the cellulose acetates prepared by traditional methods (i.e., Examples 15-1 to 15-6). The cellulose acetates prepared by traditional methods were prepared by acetylation of cellulose to make cellulose triacetate followed by H₂SO₄ catalyzed reduction of DS, a process know to yield cellulose acetates that are random copolymers. In the absence of water (dry acetone), the acetone solubility of these cellulose acetates is known to be limited to a narrow range (from about 2.48 to about 2.52).

TABLE 6 Solubility of Cellulose Acetate in Acetone (100 mg/mL). Example DS Solubility 1-1 1.82 5 1-2 2.25 4 1-3 2.44 4 2-1 0.64 5 2-2 1.49 5 2-3 1.73 5 2-4 2.01 5 2-5 2.05 5 3-1 1.81 5 3-2 2.18 1 3-3 2.39 1 3-4 2.52 2 3-5 2.62 3 3-6 2.72 3 4-1 1.58 6 4-2 1.94 2 4-3 2.15 1 4-4 2.28 1 4-5 2.63 2 5-1 1.95 2 5-2 2.21 1 5-3 2.35 1 5-4 2.52 2 5-5 2.59 2 5-6 2.60 2 5-7 2.66 3 5-8 2.67 3 6-1 2.63 2 6-2 2.75 3 6-3 2.80 3 6-4 2.87 3 6-5 2.89 3 6-6 2.96 3 8-1 1.95 3 8-2 2.15 1 8-3 2.24 1 8-4 2.33 1 8-5 2.42 1 8-6 2.56 2 8-7 2.73 2 9-1 1.74 5 9-2 2.24 1 9-3 2.38 1 9-4 2.48 2 9-5 2.60 3 9-6 2.74 3 9-7 2.82 3 15-1  2.48 1 15-2  2.46 2 15-3  2.16 3 15-4  1.99 5 15-5  1.96 5 15-6  1.80 6

Careful examination of Table 6 reveals that the cellulose acetates having a DS from about 2.15 to about 2.42 that were produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component (Examples 3-6, 8, 9) all have an acetone solubility rating of 1. That is, all of these samples yield transparent acetone solutions in which there are no visible particles. In contrast, cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the absence of a secondary component (Examples 1 and 2) have acetone solubility ratings of 4-5 regardless of DS. For example, Example 1-2 (no secondary component) has a DS of 2.25 and this cellulose acetate forms a gel in acetone while Examples 8-3 and 9-2 (which include a secondary component) have a DS of 2.24 and these cellulose acetates yield transparent acetone solutions. In agreement with what is known about cellulose acetates prepared by traditional methods, only one of the cellulose acetates examined (15-1, DS=2.48) has an acetone solubility rating of 1. Example 15-3 (DS=2.16) has an acetone solubility rating of 3, whereas Examples 4-3 and 8-2, which have similar DS values (DS=2.15), have acetone solubility ratings of 1.

This example shows that cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component having a DS of about 2.1 to about 2.4 yield transparent acetone solutions. In the absence of a secondary component, none of the cellulose acetates listed in Table 6 yield transparent acetone solutions. Furthermore, the DS range that yields transparent acetone solutions when using cellulose acetates produced by acetylation of cellulose dissolved in ionic liquids in the presence of a secondary component is broader and lower relative to cellulose acetates produced by traditional methods. Without wishing to be bound by theory, this evidence indicates that these solubility differences reflect a difference in copolymer compositions.

Example 16 Purification of [BMIm]acetate

To a 1 L 3-neck round bottom flask was added 360 mL of water, 1.30 g of acetic acid, and 5.68 g of Ba(OH)₂.H₂O. The mixture was heated to 80° C., yielding a translucent solution. To this solution was added 300 g of commercial 1-butyl-3-methylimidazolium acetate (“[BMIm]OAc”) dropwise over a period of 1 hour. The [BMIm]OAc contained 0.156 weight percent sulfur as determined by X-ray fluorescence (“XRF”). The solution was held at 80° C. for an additional hour before allowing the solution to cool to room temperature. The solids formed during the reaction were removed by centrifuging before concentrating the solution in vacuo (60-65° C., 20-80 mm Hg) to a pale yellow liquid. The liquid was extracted with two 300 mL portions of ethyl acetate (“EtOAc”). The liquid was concentrated first at 60° C. and a pressure from 20-50 mm Hg, then at 90° C. and a pressure of 4 mm Hg, finally yielding 297.8 g of a pale yellow oil. Proton NMR confirmed the formation of the [BMIm]OAc which, by XRF, contained 0.026 weight percent sulfur.

Example 17 Preparation of [BMIm]propionate

To a 1 L 3-neck round bottom flask was added 400 mL of water, 62.7 g of acetic acid, and 267 g of Ba(OH)₂.H₂O. The mixture was heated to 74° C., yielding a translucent solution. To this solution was added 100 g of commercial 1-butyl-3-methylimidazolium hydrogen sulfate (“[BMIm]HSO₄”) dropwise over a period of 1.75 hours. The solution was held at 74-76° C. for an additional 30 minutes before allowing the solution to cool to room temperature and stand overnight (approximately 14 hours). The solids formed during the reaction were removed by filtration before concentrating the solution in vacuo, which gave an oil containing solids that formed during concentration. The solids were removed by centrifuging, resulting in an amber liquid. Additional product was obtained by slurring the solids in EtOH and centrifuging. The liquids were concentrated first at 60° C. and a pressure from 20-50 mmHg, then at 90° C. and a pressure of 4 mm Hg, finally yielding 65.8 g of an amber oil. Proton NMR confirmed the formation of 1-butyl-3-methylimidazolium propionate (“[BMIm]propionate” or “[BMIm]OPr”) which, by XRF, contained 0.011 weight percent sulfur.

Example 18 Preparation of [BMIm]formate

To a 300 mL autoclave was added 25 g of 1-butylimidazole, 45.4 g (3.75 eq.) of methyl formate, and 21 mL of MeOH (2.58 eq.). The autoclave was pressurized to 1,035 kPa before heating the solution to 150° C. The contact solution was maintained at 150° C. for 18 hours. The solution was allowed to cool to room temperature before removing the volatile components in vacuo. Proton NMR of the crude reaction mixture revealed that 89% of the 1-butylimidazole was converted to 1-butyl-3-methylimidazolium formate (“[BMIm]formate” or “[BMIm]OF”). Purified [BMIm]formate was obtained by removal of residual 1-butylimidazole from the crude product by distillation.

Example 19 Conversion of [BMIm]formate to [BMIm]acetate Using Methyl Acetate

To a 300 mL autoclave was added 25 g of [BMIm]formate, 50.3 g (5.0 eq.) of methyl acetate, and 50 mL of MeOH (9 eq.). The autoclave was pressurized to 1,035 kPa before heating the solution to 170° C. The contact solution was maintained 170° C. for 15.3 hours. The solution was allowed to cool to room temperature before removing the volatile components in vacuo. Proton NMR of the reaction mixture revealed that 57% of the [BMIm]formate was converted to [BMIm]acetate.

Example 20 Conversion of [BMIm]formate to [BMIm]acetate Using Acetic Anhydride

To a 25 mL single-neck round bottom flask was added 11.1 g of [BMIm]formate. 6.15 g of acetic anhydride was then added dropwise to the [BMIm]formate. Evolution of gas was noted during the addition as well as warming of the solution (47° C.). The flask was then placed in a preheated 50° C. water bath for 45 minutes before applying a vacuum (4 mm Hg) and heating to 80° C. to remove the volatile components. Analysis of the resulting liquid by ¹H NMR indicated 100% conversion of the starting [BMIm]formate to [BMIm]acetate.

Example 21 Conversion of [BMIm]formate to [BMIm]acetate Using Acetic Acid

To a 300 mL autoclave was added 25 g of [BMIm]formate, 87.4 g (6.3 eq.) of acetic acid, and 23.1 g of MeOH (5.3 eq.). The autoclave was pressurized to 1,035 kPa before heating the solution to 150° C. The contact solution was maintained at 150° C. for 14 hours. The solution was allowed to cool to room temperature before removing the volatile components in vacuo. Proton NMR of the reaction mixture revealed that 41% of the [BMIm]formate was converted to [BMIm]acetate.

Example 22 Conversion of [BMIm]acetate to [BMIm]formate Using Methyl Formate

To a 1 L autoclave was added 100.7 g of [BMIm]acetate, 152.5 g (5 eq.) of methyl formate, and 200 mL of MeOH (9.7 eq.). The autoclave was pressurized to 1,035 kPa before heating the solution to 140° C. The contact solution was maintained at 140° C. for 18 hours. The solution was allowed to cool to room temperature before removing the volatile components in vacuo. Proton NMR of the reaction mixture revealed that 100% of the [BMIm]acetate was converted to [BMIm]formate.

Example 23 Comparison of High and Low Sulfur [BMIm]OAc 23A: Preparation of Cellulose Acetate with High Sulfur [BMIm]OAc

To a 100 mL 3-neck round bottom flask was added 32.75 g of commercial [BMIm]OAc having a relatively high sulfur content (0.156 weight percent sulfur; obtained from Fluka, a subsidiary of Sigma-Aldrich Inc., St. Louis, Mo., USA) and 1.72 g of cellulose powder. This mixture was briefly homogenized at ambient temperature before the flask was placed in a preheated 80° C. oil bath. The mixture was stirred at 80° C. and a pressure of 2 mm Hg for a period of 1.75 hours. Approximately 15 minutes were required to completely dissolve the cellulose. The straw colored solution was allowed to cool to room temperature and stand under vacuum overnight (approximately 14 hours).

To the mechanically stirred solution was added a solution of 210 mg of MSA and 5.42 g of acetic anhydride (5 eq./AGU) dropwise over a period of 23 minutes. At the end of the addition, the temperature of the contact mixture was 35° C. and the solution was dark amber in color. After 1.5 hours from the start of the addition, 5.5 g of the contact mixture was removed and the product was isolated by precipitation in MeOH. The contact mixture was then heated to 50° C. (25 minute heat up) and stirred for 1.5 hours before 6.5 g of solution was removed and poured into MeOH. The remaining contact solution was heated to 80° C. (25 minute heat up) and stirred for 2.5 hours before pouring into MeOH. All of the solids obtained by precipitation in MeOH were isolated by filtration, washed extensively with MeOH, and dried overnight at 50° C. and a pressure of 5 mm Hg.

23B: Preparation of Cellulose Acetate with Low Sulfur [BMIm]OAc

An identical reaction to 23A was conducted side-by-side using 37.02 g of [BMIm]OAc having a relatively low sulfur content (0.025 weight percent sulfur; prepared via the method described in example 16, above), 1.95 g of cellulose, 6.14 g of acetic anhydride, and 222 mg of MSA.

The amount of product isolated and the analysis of each product are summarized below in Table 7.

TABLE 7 Yield and Properties of CA Prepared in [BMIm]OAc Entry Yield (g) DS Mn Mw Mz 23A-RT 0.37 2.53 15123 54139 135397 23A-50° C. 0.45 2.65 12469 51688 123527 23A-80° C. 1.36 2.62 15828 85493 237785 23B-RT 0.29 0.80 14499 65744 301858 23B-50° C. 0.40 0.80 14768 57066 227833 23B-80° C. 1.26 0.76 16100 70293 325094

As can be seen from Table 7, above, the DS of the cellulose acetate made using the high sulfur [BMIm]OAc as solvent was higher and the molecular weight lower relative to the cellulose acetate made using the low sulfur [BMIm]OAc as solvent. Despite the increased temperature and extended contact time, the DS did not increase significantly above that observed after 1.5 hours contact time at room temperature regardless of which [BMIm]OAc was used as the solvent. Another notable aspect of this example was the color of the solutions and products. The contact solution involving high sulfur [BMIm]OAc solvent was black at all temperatures while the contact solution involving low sulfur [BMIm]OAc solvent retained the straw color typical of these solutions prior to the addition of the anhydride. The cellulose acetate solids obtained from the high sulfur [BMIm]OAc solvent were brown to black in appearance while the CA solids obtained from the low sulfur [BMIm]OAc solvent were white and provided colorless solutions upon dissolution in an appropriate solvent.

This example illustrates that impurities (e.g., sulfur or halides) in the high sulfur [BMIm]OAc can act as a catalyst in the esterification of cellulose dissolved in the [BMIm]OAc. However, the same impurities negatively impact the molecular weight and quality of the product in such a manner that the cellulose acetate has no have practical value. When cellulose is dissolved in [BMIm]OAc containing little or none of these impurities, high-quality cellulose acetate can be obtained. By introduction of an appropriate catalyst, high quality cellulose acetate with the desired DS can be obtained in a predictable manner.

Example 24 Acetylation of Cellulose in High Chloride [EMIm]OAc

1.19 g of cellulose was dissolved in 22.65 g of commercial [EMIm]OAc having a high chloride content (0.463 weight percent chloride, determined by XRF analysis) following the general procedure described in Example 23 with the exception that the mixture was not homogenized prior to heating to 80° C. The straw colored solution was mechanically stirred and preheated to 80° C. Thereafter, a solution containing 141 mg of MSA and 3.76 g of acetic anhydride (5 eq./AGU) was added dropwise over a period of 10 minutes. By the end of the addition, the contact mixture became dark brown-black. The contact solution was stirred for 2.5 hours before pouring into H₂O for precipitation. The resulting solids were isolated by filtration, washed extensively with H₂O, and dried overnight at 50° C., 5 mm Hg. This yielded 1.57 g of a brown-black cellulose acetate powder. Analysis revealed that the cellulose acetate had a DS of 2.21 and that the Mw was 42,206.

This example illustrates that [EMIm]OAc containing high levels of halides is not a suitable solvent for esterification of cellulose.

Example 25 Acetylation of Cellulose in [BMIm]Cl and [BMIm]OAc 25A: Acetylation of Cellulose in [BMIm]Cl

13.2 g of previously dried cellulose and 250.9 g of solid [BMIm]Cl (mp=70° C.) were combined in a glass jar. The glass jar was placed in a preheated 40° C. vacuum oven and heated to 80° C. over a period of 3 hours. The sample was allowed to stand under vacuum at 80° C. for a period of approximately 14 hours before the jar was removed. The sample was immediately homogenized, yielding a clear solution of cellulose.

To a 100 mL 3-neck round bottom flask was added 33.6 g of the cellulose solution prepared above. The flask was placed in a preheated 80° C. oil bath and a vacuum was applied (7-8 mm Hg). The solution was then stirred for a period of 21 hours while at 80° C. and under vacuum. The cellulose solution was then allowed to cool to 38° C.; the temperature could not be lowered further due to the solution viscosity. 5.3 g of acetic anhydride (5 eq./AGU) was then added dropwise over a period of 7 minutes. The contact mixture was then stirred at a temperature of 32-35° C. for 2 hours. Thereafter, a small amount of the solution was removed and poured into MeOH resulting in precipitation of the cellulose acetate. The remaining contact mixture was then heated to 50° C. and held at that temperature for 1.6 hours before removing a small amount of the solution, which was poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was then heated to 80° C. and held at that temperature for 1.5 hours before allowing the solution to cool and adding 60 mL of MeOH to precipitate the cellulose acetate. All three samples were washed extensively with MeOH then dried at 50° C. and a pressure of 5 mm Hg overnight.

25B: Acetylation of Cellulose in [BMIm]Cl with Zn(OAc)₂

To a 100 mL 3-neck round bottom flask was added 31.3 g of the cellulose solution prepared above. The same general protocol used in the previous reaction (25A) was followed with the exception that Zn(OAc)₂ (0.05 eq./AGU) was added to the cellulose solution prior to cooling to 38° C.

25C: Acetylation of Cellulose in [BMIm]OAc

To a 100 mL 3-neck round bottom flask was added 27.41 g of low sulfur [BMIm]OAc (as prepared in example 16) and 1.44 g of cellulose. The flask was placed in a preheated 80° C. oil bath and the mixture was allowed to stir overnight (approximately 14 hours) under a 2 mm Hg vacuum.

After cooling the solution to room temperature (25.1° C.), Ac₂O (5 eq./AGU) was added to the cellulose solution dropwise over a period of 25 minutes. The contact mixture was then stirred for 1.8 hours at room temperature. Thereafter, a small portion of the solution was removed and poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was heated to 50° C. and maintained at that temperature for 1.5 hours before removing a small portion of the solution, which was then poured into MeOH to precipitate the cellulose acetate. The remaining contact mixture was heated to 80° C. and maintained at that temperature for 2.5 hours before cooling and pouring into MeOH. All three samples were washed extensively with MeOH then dried at 50° C. and a pressure of 5 mm Hg overnight.

25D: Acetylation of Cellulose in [BMIm]OAc with Zn(OAc)₂

To a 100 mL 3-neck round bottom flask was added 25.55 g of low sulfur [BMIm]OAc (as prepared in example 16, above) and 1.35 g of cellulose. The flask was placed in a preheated 80° C. oil bath and the mixture was allowed to stir overnight (approximately 14 hours) under a 2 mm Hg vacuum. The same general protocol used in the previous reaction (25C) was followed, with the exception that Zn(OAc)₂ (0.05 eq./AGU) was added to the cellulose solution prior to cooling to room temperature.

Analyses of the cellulose acetates isolated from these 4 comparative reactions (25A-25D) are summarized below in Table 8.

TABLE 8 Physical properties of CA prepared in [BMIm]Cl or [BMIm]OAc Entry Solvent Catalyst DS Mn Mw Mz 25A-RT [BMIm]Cl none 0.57 7753 16777 32019 25A-50° C. [BMIm]Cl none 1.42 9892 19083 33019 25A-80° C. [BMIm]Cl none 2.27 11639 21116 34138 25B-RT [BMIm]Cl Zn(OAc)₂ 1.77 8921 19468 36447 25B-50° C. [BMIm]Cl Zn(OAc)₂ 2.32 7652 18849 38367 25B-80° C. [BMIm]Cl Zn(OAc)₂ 2.75 7149 18964 38799 25C-RT [BMIm]OAc none 1.17 7039 41534 118265 25C-50° C. [BMIm]OAc none 1.17 7839 45116 136055 25C-80° C. [BMIm]OAc none 1.17 7943 48559 165491 25D-RT [BMIm]OAc Zn(OAc)₂ 2.27 8478 47730 125440 25D-50° C. [BMIm]OAc Zn(OAc)₂ 2.30 11017 53181 136619 25D-80° C. [BMIm]OAc Zn(OAc)₂ 2.34 12096 56469 141568

This comparative example illustrates a number of important points. In the case of [BMIm]Cl, the DS of the cellulose acetate increases with each contact time-temperature from 0.57 to 2.27. The same trend is observed with [BMIm]Cl+Zn(OAc)₂ with the exception that the DS at each contact time-temperature is higher due to the Zn(OAc)₂, which acts as a catalyst. In the case of [BMIm]OAc, with or without Zn(OAc)₂ the DS does not significantly change from that obtained at room temperature with increasing contact time-temperature; however, the total DS is significantly increased by the action of the Zn(OAc)₂. This unexpected observation indicates that acetylation of cellulose dissolved in [BMIm]OAc is much faster at lower temperatures relative to that observed in acetylation of cellulose dissolved in [BMIm]Cl. It should also be noted that a transition metal like Zn is very effective in catalyzing or promoting the acylation of cellulose dissolved in ionic liquids. Finally, it should also be noted that the molecular weights of the cellulose acetates obtained by acetylation of cellulose dissolved in [BMIm]OAc is significantly greater relative to when cellulose is dissolved in [BMIm]Cl.

Example 26 Preparation of Mixed Cellulose Esters

The following general procedure was used to prepare cellulose mixed esters. To a 100 mL 3-neck round bottom flask was added the desired amount of a selected 1-butyl-3-methylimidazolium carboxylate. While stirring at room temperature, 5 weight percent cellulose was slowly added to the ionic liquid. After the cellulose was dispersed in the ionic liquid, the flask was placed under vacuum (2-5 mm Hg) and the contact mixture was heated to 80° C. The contact solution was then stirred for a period of approximately 2 hours before adding 0.1 eq./AGU of Zn(OAc)₂. The contact solution was stirred for approximately 30 minutes before the solution was allowed to cool to room temperature and stand overnight (approximately 14 hours).

The contact solution was then placed under N₂, followed by the dropwise addition of 5 eq./AGU of the desired carboxylic anhydride. When the addition was complete, the flask was placed in a preheated 40° C. oil bath. The contact mixture was stirred for 5 hours before the solution was allowed to cool and poured into MeOH for precipitation. The resulting solids were isolated by filtration, washed extensively with MeOH, and dried in vacuo at 50° C. and a pressure of 5 mm Hg. The products were then characterized by ¹H NMR, the results of which are summarized below in Table 9.

TABLE 9 Cellulose Esters Prepared in Different Alkyl Imidazolium Carboxylates Entry Ionic liquid Anhydride DS_(Total) DS_(Ac) DS_(Pr) DS_(Bu) 1 [BMIm]OAc Bu₂O 2.40 2.43 — 0.45 2 [BMIm]OBu Ac₂O 2.43 2.30 — 0.70 3 [BMIm]OPr Bu₂O 2.52 — 1.95 1.05

Note that in Table 9, above, the DS of the individual substituents have been normalized to 3.0 for comparison purposes. As this example illustrates, when cellulose is dissolved in an alkyl imidazolium carboxylate and contacted with a carboxylic anhydride containing a different acyl group from the anion of the ionic liquid, the product is a mixed cellulose ester. That is, the cellulose substituents come from the added anhydride and from the alkyl imidazolium carboxylate. In effect, the alkyl imidazolium carboxylate is acting as an acyl donor to the cellulose.

Example 27 Removal of Carboxylic Acid

To each vessel of a 4 vessel Multimax high pressure reactor equipped with an in situ infrared probe was added previously dried [BMIm]OAc, 1 molar equivalent of acetic acid based on ionic liquid, different molar amounts of MeOH based on acetic acid, and, optionally, a catalyst (2 mol %). The pressure in each vessel was increased to 5 bar over a 3 minute period, followed by increasing the contact temperature to 140° C. over a 25 minute period. The contact mixtures were then held at 140° C. for 10-15 hours as the reaction in each vessel was monitored by infrared spectroscopy. The vessels were then allowed to cool to 25° C. over a 30 minute period. The contents of each vessel were then concentrated in vacuo to remove all volatile components before analyzing each sample by proton NMR. FIG. 16 shows a plot of weight percent acetic acid versus time as determined by infrared spectroscopy; the final concentration of acetic acid was confirmed by ¹H NMR. FIG. 16 shows that in all cases, the reactions were complete within 9-10 hours. The most significant factor affecting the rates and extent of reaction was the number of molar equivalents of MeOH. The weight percent of acetic acid remaining in the [BMIm]OAc ranged from 7.4 weight percent to 2.2 weight percent.

With typical distillation techniques, it is extremely difficult to get excess carboxylic acid concentration below 1 molar equivalent based on carboxylated ionic liquid. In the case of acetic acid in [BMIm]OAc, this corresponds to about 23 weight percent acetic acid. This example shows that, by conversion of the acetic acid to methyl acetate, which is much more easily removed, the amount of residual acetic acid can be reduced well below 23 weight percent. The amount of acetic acid removed will depend upon several factors, including the amount of acetic acid initially present, concentration of MeOH, contact times, and contact temperature. As shown in this example, it is not necessary to remove all of the residual carboxylic acid; in many instances, it is desirable to retain residual carboxylic acid.

Example 28 Solubility of Cellulose in Ionic Liquid

Samples of 1-butyl-3-methylimidazolium acetate containing different amounts of acetic acid in 2 ounce jars were dried at 80° C.±5° C. at a pressure of about 3 mm Hg overnight (approximately 14 hours). Examples 28-1 through 28-5 were prepared by the method of Example 27. Examples 28-6 through 28-8 were prepared by adding a known amount of acetic acid to neat [BMIm]OAc (see Table 10). Cellulose (5 weight percent, DP 335), was added to each [BMIm]OAc sample, followed by brief homogenization of each sample. Each sample was then transferred to a microwave reaction vessel, which was then capped with an air tight lid and placed in a 48 cell microwave rotor. The rotor was placed in a Anton Paar Synthos 3000 microwave and the cellulose-[BMIm]OAc mixtures were heated to 100° C. using a 3 minute ramp and held for 10 minutes before heating to 120° C. using a 3 minute ramp and held for 5 minutes. Inspection of each vessel indicated that the cellulose in each sample was dissolved in the [BMIm]OAc.

TABLE 10 Solubility of Cellulose in [BMIm]OAc Example HOAc (wt %) IL (g) Soluble 28-1 2.2 6.16 y 28-2 2.8 8.78 y 28-3 5.8 8.48 y 28-4 6.6 8.48 y 28-5 7.4 8.15 y 28-6 10.0 10.23 y 28-7 12.5 10.26 y 28-8 14.5 10.18 y

The foregoing two examples illustrate that excess residual carboxylic acid in ionic liquids can be reduced by the method of Example 27 and that the recycled ionic liquid containing residual carboxylic acid can then be used to dissolve cellulose so that the solutions can be used for preparing cellulose esters. This example also illustrates that cellulose can be dissolved in an ionic liquid containing up to about 15 weight percent carboxylic acid.

Example 29 Recycling of Ionic Liquid

To a 500 mL flat bottom kettle was added 299.7 g of [BMIm]OAc. A 4-neck top was placed on the kettle and the kettle was fitted with an N₂/vacuum inlet, a React IR 4000 diamond tipped IR probe, a thermocouple, and equipped for mechanical stirring. The kettle contents were placed under vacuum (approximately 4.5 mm Hg) and heated to 80° C. using an oil bath. The removal of water from the [BMIm]OAc was followed by analysis by infrared spectroscopy (FIG. 17). After about 16 hours, the oil bath was removed and the kettle contents were allowed to cool to room temperature.

To the ionic liquid was added 3.77 g of Zn(OAc)₂ (0.1 eq.). The mixture was stirred for about 75 minutes to allow the Zn(OAc)₂ to dissolve before slowly adding 33.3 g (10 weight percent) of previously dried cellulose (DP 335) over a 26 minute period. The mixture was stirred at room temperature for about 4 hours, after which time no particles or fiber were visible in the translucent solution; infrared spectroscopy indicated that all of the cellulose was dissolved (FIG. 18). The solution was then heated to 80° C. By the time the temperature reached 60° C., the translucent solution was completely clear. After reaching 80° C., the solution was cooled to room temperature.

To the cellulose-[BMIm]OAc solution was added 104.9 g of Ac₂O (5 eq.) dropwise over a 70 minute period. During the Ac₂O addition, the contact temperature rose from an initial value of 21.4° C. to a maximum value of 44.7° C. Infrared spectroscopy indicated that the Ac₂O was consumed nearly as fast as it was added (FIG. 19). When all of the Ac₂O was added, the contact temperature immediately began to decline and the contact mixture went from a fluid liquid to a flaky gel. Stirring was continued for an additional 3.5 hours, but no changes were observed by infrared spectroscopy.

The gel was then added to 800 mL of MeOH while stirring, resulting in the precipitation of a white powder. After separation by filtration, the solids were then washed 3 times with approximately 800 mL portions of MeOH, then 1 time with approximately 900 mL of MeOH containing 11 weight percent of 35% H₂O₂. The solids were then dried at 40° C. and a pressure of 3 mm Hg yielding 60.4 g of a white solid. Analysis by proton NMR and GPC revealed that the solid was a cellulose triacetate (DS=3.0) having a Mw of 58,725. The cellulose triacetate (13.6 weight percent) was completely soluble in 90:10 CH₂Cl₂:MeOH, from which clear films can be cast. Such films are useful in constructing liquid crystalline displays and in photographic film base.

The precipitation and wash liquids from the cellulose triacetate isolation were concentrated in vacuo at 50° C. until the vacuum dropped to about 3 mm Hg, which yielded 376.6 g of a liquid. Proton NMR indicated that the liquid was [BMIm]OAc containing approximately 17 weight percent excess acetic acid. To a 1.8 L autoclave was added the 376.6 g of recovered [BMIm]OAc along with 483.8 g of MeOH. The pressure in the autoclave was adjusted to 100 psi with N₂ before the vessel contents were heated to 140° C. and held for 9 hours. After cooling to room temperature, the volatile components were removed in vacuo, which produced 299.8 g of a liquid. Proton NMR showed the liquid to be [BMIm]OAc containing 2.6 weight percent excess acetic acid. When the weight of the initial [BMIm]OAc was corrected for water content, the amount of recycled [BMIm]OAc corresponds to 100% recovery.

This example illustrates that cellulose triacetate can rapidly be prepared from cellulose that has been dissolved in ionic liquids. This example also indicates that excess carboxylic acid can be removed from the ionic liquid and the recycled ionic liquid can be recovered in high yield. The recycled ionic liquid can then be used to dissolve cellulose so that the solutions can be used again for preparing cellulose esters.

Example 30 Anion Exchange to Form Carboxylated Ionic Liquid

To a vial containing a small magnetic stir bar was added 4.2 g of [BMIm]formate. An iC10 diamond tipped IR probe was inserted into the vial so that the reaction could be monitored in situ by infrared spectroscopy. To the [BMIm]formate was added 0.5 eq. of Ac₂O in one portion. As FIGS. 20 and 21 illustrate, 50% of the [BMIm]formate was almost immediately converted to [BMIm]OAc. Additional spectra were collected to allow the system to stabilize before adding another 0.5 eq. of Ac₂O in one portion. Infrared spectroscopy indicated that the remaining [BMIm]formate was almost immediately converted to [BMIm]OAc.

This example shows that [BMIm]formate is rapidly converted to [BMIm]OAc with the addition of Ac₂O. The reaction rate is so rapid that the [BMIm]formate can be titrated with Ac₂O until no gas is evolved.

Example 31 Effect of MeOH During Anion Exchange

To a vial containing a small magnetic stir bar was added 3.15 g of [BMIm]formate. An iC10 diamond tipped IR probe was inserted into the vial so that the reaction could be monitored in situ by infrared spectroscopy. To the [BMIm]formate was added 2 eq. of MeOH. After the system thermally stabilized, 1 eq. of Ac₂O was added to the [BMIm]formate in one portion. As FIGS. 22 and 23 illustrate, infrared spectroscopy indicated that the [BMIm]formate was almost immediately converted to [BMIm]OAc.

This example shows that the reaction of [BMIm]formate with Ac₂O to form [BMIm]OAc is much faster than the reaction of Ac₂O with MeOH to form MeOAc. Hence, it is not necessary to remove MeOH from [BMIm]formate prior to converting the [BMIm]formate to [BMIm]OAc.

Example 32 Effects of Water Modification and MSA

A 3-neck 250 mL round bottom flask, fitted with two double neck adapters for a total of five ports, was equipped for mechanical stirring, and further included an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) and an N₂/vacuum inlet. To the flask was added 62.37 g of [BMIm]OAc.

To 5.06 g (7.5 weight percent) of cellulose (DP 335) was added 20.68 g of water. After hand mixing, the cellulose was allowed to stand in the water for 65 minutes at 60° C. before filtering, which yielded 10.78 g of a wet cellulose cake. The water-wet cellulose was then added in small portions to the [BMIm]OAc over a period of 5 minutes. Within 5 minutes, the cellulose was well dispersed in the ionic liquid (a few small clumps were visible). The mixture was stirred for 7 minutes before a preheated 80° C. oil bath was raised to the flask. The mixture was then stirred for 28 minutes (visually, nearly all of the cellulose was dissolved) before slowly placing the flask contents under vacuum with the aid of a bleed valve (FIG. 24). After 1.5 hours, the vacuum was at 1.9 mm Hg. The clear mixture was then stirred overnight under vacuum at 80° C.

The clear solution was allowed to cool to room temperature after 15 hours and 45 minutes from the point of cellulose addition. Thereafter, a mixture of 12.11 g (3.8 eq.) of Ac₂O and 600 mg of MSA was added to the solution dropwise over a period of 28 minutes. The maximum temperature reached during the Ac₂O addition was 46° C. Eight minutes after completing the Ac₂O addition, a preheated 50° C. oil bath was raised to the flask. The mixture was stirred for 16 minutes, and then 1.46 g of water was slowly added to the solution over a period of 2 minutes. The solution was then stirred for 17 minutes followed by adding an additional 0.47 g of water. The solution was then stirred for 5 hours and 9 minutes before cooling the solution to room temperature. The reaction was sampled (see FIG. 25) throughout the contact period by removing 6 to 10 g aliquots of the reaction mixture and precipitating in 100 mL of MeOH. The solid from each aliquot was washed once with a 100 mL portion of MeOH then twice with 100 mL of MeOH containing 8 weight percent of 35% H₂O₂. The samples were then dried at 60° C. and a pressure of 5 mm Hg overnight.

This example illustrates a number of benefits of the methods employed herein. As can be seen from FIG. 24, water-wet cellulose can be readily dissolved in carboxylated ionic liquid even when a significant amount of water still remains in the ionic liquid. As shown in FIG. 25, the rate of reaction in the acylation of this cellulose in a carboxylated ionic liquid is very rapid; a significant concentration of Ac₂O is never observed indicating that the Ac₂O is consumed nearly as fast as it is added. The rapid rates of reaction can lead to a much different monomer distribution relative to that observed in other ionic liquids. For example, FIG. 26 compares the proton resonances of the protons attached to the anhydroglucose rings of cellulose acetates (DS=2.56) prepared from cellulose dissolved in [BMIm]OAc (top spectrum) and dissolved in [BMIm]Cl (bottom spectrum). The major resonances in the top spectrum centered near 5.04, 5.62, 4.59, 4.29, 4.04, 3.73, and 3.69 correspond to trisubstituted monomers. In the bottom spectrum, there are much less of these resonances relative to the other type of monomer resonances. This discovery is significant in that the rapid rates of reaction provide a means to produce nonrandom cellulose ester copolymers with different levels of block segments. The extent and the size of the block segments depends upon factors such as mixing, prior water treatment or no water treatment of the cellulose, concentration and type of catalyst, contact temperature, and the like.

As shown in FIG. 25, 3 samples were taken prior to the addition of water. These 3 samples ranged in DS from 2.48-2.56 and, at 10 weight percent in acetone, they were soluble giving slightly hazy solutions (solubility rating of 2). In contrast, the 2 samples taken after water addition (DS about 2.52) were insoluble in acetone (solubility rating of 6). FIG. 27 compares the ring proton resonances for cellulose acetates prepared from cellulose dissolved in [BMIm]OAc before and after addition of water. The top spectrum corresponds to a cellulose acetate after water addition (DS=2.53) and the bottom spectrum corresponds to a cellulose acetate before water addition (DS=2.56). The differences between these 2 spectra are consistent with different monomer compositions in the copolymers.

Example 33 Production of Cellulose Triacetate in [EMIm]OAc

To a 3-neck 100 mL round bottom flask equipped for mechanical stirring and having an N₂/vacuum inlet was added 34.63 g of 1-ethyl-3-methylimidazolium acetate (“[EMIm]OAc”). While stirring rapidly, 6.11 g (15 weight percent) of dry cellulose powder (DP 335) was added to the flask. The flask was then placed in a 90° C. oil bath and the mixture was stirred for 10 minutes, followed by application of vacuum (2 mm Hg). After 50 minutes, the oil bath temperature was increased to 100° C. After 2 hours and 25 minutes, the oil bath was turned off and the solution was left standing under vacuum overnight.

To the cellulose solution was added a mixture of 731 mg of MSA and 19.24 g (5 eq.) of Ac₂O dropwise over a period of 40 minutes. Initially, the solution was stirred slowly so that the solution did not bunch around the stir shaft. As the Ac₂O was added, the solution viscosity dropped; after adding about 5 mL, the solution stirred easily and the stir rate was increased. During the addition, the solution viscosity did not increase and no localized gels were observed until the last few drops of Ac₂O were added. At this point the entire contact mixture suddenly gelled. The contact temperature rose from 24.1° C. to 47.5° C. by the end of addition. During the addition, there was little change in the color of the solution. After the reaction mixture gelled, 11.54 g of the reaction mixture was removed with a spatula and solids were obtained by precipitation in MeOH (Sample 1). The flask containing the remaining reaction mixture was then placed in a preheated 50° C. oil bath. After 20 minutes at 50° C., there was no evidence of the gel softening. Hence, the gel was allowed to cool to room temperature and 50 mL of MeOH was added to the flask. The flask contents were then placed into 400 mL of MeOH, which yielded a white precipitate (Sample 2). Both fractions were processed by stirring the initial slurry for approximately 1 hour before isolating the solids by filtration. The solids were washed by taking them up in 300 mL of MeOH and stirring the slurry for approximately 1 hour before the solids were isolated by filtration. The solids were twice taken up in 300 mL of 12:1 MeOH:35% H₂O₂ and the slurry was stirred for approximately 1 hour before the solids were isolated by filtration. The solids were then dried overnight at 50° C. and a pressure of about 20 mm Hg.

The combined yield for Samples 1 and 2 was 10.2 g of a white solid. Analysis by ¹H NMR showed that Samples 1 and 2 were identical and that they were cellulose triacetates with a DS of 3.0. By GPC, both samples had a Mw of about 54,000.

This example shows that cellulose triacetate can rapidly be prepared from cellulose dissolved in [EMIm]OAc. Cellulose triacetate can be used to prepare film useful in liquid crystalline displays and photographic film base.

Example 34 Immiscible Co-Solvent Effect on IL Viscosity

To a 3-neck 50 mL round bottom flask equipped for mechanical stirring and having an N₂/vacuum inlet was added 20.03 g of [EMIm]OAc. While stirring rapidly, 1.05 g of dry cellulose powder (DP 335) was added to the flask. The flask was then placed under vacuum (2 mm Hg) and placed in an oil bath preheated to 90° C. After 1 hour and 45 minutes, the oil bath temperature was increased to 100° C. and stirred for an additional 55 minutes (2 hours and 40 minutes total contact time) before allowing the solution to cool to ambient temperature while under vacuum.

To the resulting cellulose solution was added 20 mL of methyl acetate, yielding a 2-phase reaction mixture. While stirring rapidly, a mixture of 131 mg of MSA and 4.63 g of Ac₂O was added dropwise to the solution over a period of 10 minutes. The contact temperature was increased from 23.3° C. to 35.4° C. and, at the end of the addition, the contact mixture was a single phase whose viscosity was much lower than that of the original cellulose-[EMIm]OAc solution. Twenty-five minutes after beginning the addition, the flask was placed in a preheated 50° C. oil bath. The contact mixture was stirred for 2 hours at 50° C. and thereafter allowed to cool to ambient temperature over a period of 50 minutes. The product was precipitated in 350 mL of MeOH and the slurry was stirred for approximately 1 hour before the solids were isolated by filtration. The solids were then washed by taking them up in 300 mL of MeOH and stirring the slurry for about 1 hour before the solids were isolated by filtration. Twice, the solids were taken up in 300 mL of 12:1 MeOH:35% H₂O₂ and the slurry was stirred for about 1 hour before the solids were isolated by filtration. The solids were then dried overnight at 50° C. and a pressure of about 20 mm Hg, which yielded 1.68 g of a white solid. Analysis by ¹H NMR revealed that the solid was a cellulose acetate having a DS of 2.67. Analysis by GPC indicated that the cellulose acetate had a Mw of 51,428 and a Mw/Mn of 4.08.

This example shows that a cellulose solution in an ionic liquid can be contacted with an immiscible or sparingly soluble co-solvent without causing precipitation of the cellulose. Upon contact with an acylating reagent, the cellulose is esterified, thus changing the solubility of the now cellulose ester-ionic liquid solution with the formerly immiscible co-solvent so that the contact mixture becomes a single phase. The resulting single phase has a much lower solution viscosity than the initial cellulose-ionic liquid solution. This discovery is significant in that highly viscous cellulose solutions can now be used to make cellulose esters while still maintaining the ability to mix and process the solution. This discovery also provides a way to process highly viscous cellulose-ionic liquid solutions at lower contact temperatures. The cellulose ester product can be isolated from the new single phase by conventional means. The cellulose ester product has desirable degrees of substitution, molecular weights, and solubility in solvents such as acetone, and can be readily melt processed when plasticized with plasticizers such as diethyl phthalate and the like.

Example 35 Immiscible Co-Solvent Biphasic to Single Phase

A 3-neck 100 mL round bottom flask containing 28.84 g of a 5 weight percent cellulose solution in [BMIm]Cl was equipped for mechanical stirring and with an N₂/vacuum inlet. The flask was placed in a preheated 80° C. oil bath and the flask contents were placed under vacuum (approximately 7 mm Hg) for 2 hours. To the solution was added 25 mL of methyl ethyl ketone that had been previously dried over 4A molecular sieves resulting in two well defined phases. To the biphasic mixture was added 4.54 g of Ac₂O while stirring vigorously. After about 75 minutes, the contact mixture appeared to be homogeneous. After 2.5 hours, the contact mixture was allowed to cool to room temperature. Phase separation did not occur even when a small amount of water and methyl ethyl ketone was added to the homogeneous mixture. The product was isolated by addition of the contact mixture to 200 mL of MeOH followed by filtration to separate the solids. The solids were washed twice with MeOH and three times with water before they were dried at 50° C. and a pressure of about 5 mm Hg. Analysis by ¹H NMR and by GPC revealed that the product was a cellulose acetate with a DS of 2.11 and Mw of 50,157.

This example shows that a cellulose solution in an ionic liquid, such as [BMIm]Cl, can be contacted with an immiscible or sparingly soluble co-solvent, such as methyl ethyl ketone, without causing precipitation of the cellulose. Upon contact with an acylating reagent, the cellulose is esterified, which changes the solubility of the now cellulose ester-ionic liquid solution with the formerly immiscible co-solvent so that the contact mixture became a single phase from which the cellulose ester could be isolated by precipitation with an alcohol.

Example 36 Color of Cellulose Esters

Color development during esterification of cellulose dissolved in ionic liquids depends on a number of factors. These factors include the type of ionic liquid used to dissolve the cellulose, impurities contained in the ionic liquid, type of cellulose, the presence or absence of binary components (see, e.g., Example 3), cellulose dissolution contact time and temperature, and esterification contact time and temperature, among others. Understanding these factors and the mechanisms involved in color formation is the best way to prevent color formation. However, even when the best practices are followed, colored product is still often obtained. The inventors have found that color formation can be reduced by contacting the cellulose ester with a bleaching agent while dissolved in ionic liquid and/or after separation of the cellulose ester from the ionic liquid.

Table 11, below, compares the color values of several cellulose esters prepared according to the following general method. To a 7.5 weight percent solution of cellulose dissolved in ionic liquid was added a mixture of 2.9 equivalents of acylating reagent (i.e., acetic anhydride, propionic anhydride, and/or butyric anhydride) and 0.1 equivalents of a binary component. The type of ionic liquid and binary component (if present) employed for each sample are indicated in Table 11, below. After 65 minutes, in situ IR indicated that the reaction was complete. Entries 1-6 of Table 11 were then isolated by precipitation in water, washed with water, and dried.

Entry 9 of Table 11 was subjected to a bleaching process while still in solution. Thus, to the solution prepared as described above was added 0.75 weight percent of a 2.25 weight percent solution of potassium permanganate dissolved in methanol. The mixture was stirred for 2 hours before the cellulose ester was isolated by precipitation in water, washed with water, and dried.

Entries 7, 8, and 10-16 of Table 11 were subjected to a bleaching process following isolation. Thus, after completing the reaction described above, the cellulose ester was isolated from the ionic liquid by precipitation in methanol followed by washing with water. Thereafter, the resulting solids were twice taken up in 300 mL of 12:1 MeOH:35% H₂O₂ and the slurry was stirred for about 1 hour before the solids were isolated by filtration.

TABLE 11 Color Evaluation of Cellulose Ester Solutions Ionic liquid-(binary Cellulose Entry L* a* b* ΔE component) Ester^(‡) Bleach 1 97.65 −2.24 11.07 11.54 [BMIm]Cl-(MSA)^(†) CA None 2 94.28 −1.85 17.83 18.83 [BMIm]Cl-(MSA) CA None 3 93.56 −1.74 17.84 19.06 [BMIm]Cl-(MSA) CA None 4 46.56 41.45 77.89 103.19 [BMIm]OAc-(MSA) CA None 5 50.35 35.44 89.8 108.59 [BMIm]OAc CA None 6 74.52 12.66 85.28 89.91 [BMIm]OAc CAP None 7 96.89 −1.44 10.10 10.68 [BMIm]Cl-(MSA) CA H₂O₂ 8 98.24 −1.09 4.37 4.85 [BMIm]Cl-(MSA) CA H₂O₂ 9 98.37 −1.04 5.69 6.02 [BMIm]Cl-(MSA) CA KMnO₄ 10 98.43 −3.00 10.72 11.24 [EMIm]OAc CA H₂O₂ 11 98.10 −3.06 10.34 10.95 [BMIm]OAc CA H₂O₂ 12 98.44 −1.51 5.87 6.27 [BMIm]OBu CAB H₂O₂ 13 97.91 −2.43 10.68 11.15 [EMIm]OAc-(MSA) CA H₂O₂ 14 99.44 0.00 0.58 0.87 [BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 15 99.02 0.05 1.63 1.94 [BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 16 99.32 −0.48 1.98 2.16 [BMIm]OPr-(MSA) CP H₂O₂ ^(†)MSA = methane sulfonic acid ^(‡)CA = cellulose acetate CAP = cellulose acetate propionate CAB = cellulose acetate butyrate CP = cellulose propionate

As can be seen in Table 11, comparing entries 1-3 to entries 4-6 (each having no bleaching), it is evident that more color is created during cellulose esterification when the anion of the ionic liquid is a carboxylate compared to when the anion is a halide. When the anion was a halide, and in the absence of bleaching, the L* and ΔE values ranged from 93.6-97.7 and 19.1-11.5, respectively (entries 1-3). Bleaching with H₂O₂ after separation of the cellulose ester from the ionic liquid increased the a* values and decreased the b* values, resulting in improvement of color which is reflected in a lower ΔE values (entries 7 and 8). Bleaching the cellulose ester while it is dissolved in the ionic liquid led to a similar improvement in color (entry 9). In this case, L* and a* increased while b* decreased resulting in a ΔE value of 6.02.

When the anion was a carboxylate, in the absence of bleaching, L* and ΔE ranged from 46.6-74.5 and 108.6-89.9, respectively (entries 4-6). Bleaching with H₂O₂ after separation of the cellulose ester from the ionic liquid led to a dramatic improvement in color. The L* values increased while the a* and b* values decreased, resulting in ΔE values of 0.9-11.2 (entries 10-16). Accordingly, this example illustrates that contacting a cellulose ester with a bleaching agent while dissolved in ionic liquid or after separation of the cellulose ester from the ionic liquid can lead to very significant improvements in color.

Example 37 Viscosities of Cellulose-Ionic Liquid Solutions with Miscible Co-Solvents

Solutions of cellulose dissolved in [BMIm]Cl containing different levels of acetic acid were prepared according to the following general procedure. [BMIm]Cl was added to a 3-neck, 50 mL round bottom flask equipped for mechanical stirring and with an N₂/vacuum inlet. The flask was placed in a preheated 80° C. oil bath and the flask contents were placed under vacuum (0.8 mm Hg) for 1.7 hours. Thereafter, either 0, 5, or 10 weight percent of acetic acid was added to the solution before allowing it to cool to room temperature. Next, 5 weight percent of cellulose was added to the solution and was then heated again to 80° C. The mixture was stirred until a homogeneous solution was obtained (about 80 minutes). The solution was then cooled to room temperature.

FIG. 28 compares the viscosities of cellulose solutions containing no acetic acid, 5 weight percent acetic acid, and 10 weight percent acetic acid at 25, 50, 75, and 100° C. As illustrated in FIG. 28, the viscosity of the cellulose-[BMIm]Cl-5 weight percent acetic acid solution is significantly less than that of cellulose-[BMIm]Cl at all temperatures. For example, at 25° C. and 0.2 rad/sec, the viscosity of the cellulose-[BMIm]Cl-5 weight percent acetic acid solution is 466 poise versus 44,660 poise for the cellulose-[BMIm]Cl solution. Comparing the viscosities of the cellulose-[BMIm]Cl-10 weight percent acetic acid solution to the cellulose-[BMIm]Cl-5 weight percent acetic acid and cellulose-[BMIm]Cl solutions at 25° C., it is evident that the viscosity of the cellulose-[BMIm]Cl-10 weight percent acetic acid solution is less than that of the cellulose-[BMIm]Cl solution but greater than that of the cellulose-[BMIm]Cl-5 weight percent acetic acid solution. At 25° C. and 0.2 rad/sec, the viscosities of the cellulose-[BMIm]Cl-10 weight percent acetic acid, cellulose-[BMIm]Cl-5 weight percent acetic acid, and cellulose-[BMIm]Cl solutions are 22,470, 466, and 44,660 poise, respectively. With increasing temperature, the differences in the viscosities between the cellulose-[BMIm]Cl-10 weight percent acetic acid and cellulose-[BMIm]Cl solutions diminish and the observed viscosities apparently depend upon the shear rate.

This example shows that the viscosity of a cellulose-ionic liquid solution can be dramatically altered by adding a miscible co-solvent such as a carboxylic acid to the solution. The viscosity drops with increasing miscible co-solvent reaching a minimum before increasing again as additional co-solvent is added.

Example 38 Viscosities of Cellulose-Ionic Liquid Solutions with Immiscible Co-Solvents

In order to determine the impact of an immiscible co-solvent (which tends to form two layers with the initial cellulose-ionic liquid solution) on solution viscosity, it is necessary to convert the cellulose to a cellulose ester prior to making the viscosity measurement.

A cellulose solution was prepared as follows. To a 3-neck, 100 mL round bottom flask equipped for mechanical stirring and with an N₂/vacuum inlet was added 33.18 g of [BMIm]CL. While stirring rapidly, 1.75 g of dry cellulose (5 weight percent) were added to the flask. The flask was then placed under vacuum (2 mm Hg) and placed in an oil bath preheated to 80° C. After 30 minutes in the oil bath, all of the cellulose was dissolved. The oil bath and stirring were turned off and the solution was left under vacuum overnight.

To the resulting cellulose solution was added 30 mL of methyl ethyl ketone resulting in a 2-phase reaction mixture. While stirring rapidly, a mixture of 104 mg of MSA and 5.51 g of Ac₂O was added dropwise over a period of 3 minutes. At the end of the addition, the reaction mixture had two phases. After stirring for about 70 minutes from the start of addition, the reaction mixture was a single phase; the viscosity of the phase was much less than that of the original cellulose solution. Stirring was continued for an additional 150 minutes before 10.9 g of the solution was removed for viscosity measurements. The remaining solution was then cooled to room temperature and the product was isolated by precipitating in 350 mL of MeOH. The resulting slurry was stirred for about 1 hour before the solids were isolated by filtration. The solids were then washed 4 times with 250 mL of MeOH. The solids were then dried overnight at a temperature of 50° C., and a pressure of 5 mm Hg, which gave 1.66 g of a white solid. Analysis revealed that the solid was the expected cellulose acetate. A second reaction was conducted in the same fashion except that the co-solvent (i.e., methyl ethyl ketone) was omitted. Again, a sample was removed for viscosity measurements just prior to precipitation of the cellulose acetate.

FIG. 29 compares the solution viscosity of the contact mixtures with and without an immiscible co-solvent at 25° C. As can be seen in FIG. 29, inclusion of an immiscible co-solvent dramatically reduces the viscosity of the solution. For example, at 25° C. and 1 rad/sec, inclusion of methyl ethyl ketone resulted in a solution with a viscosity of 24.6 poise versus 6,392 poise for the solution without methyl ethyl ketone.

Example 39 Impact of Miscible Co-Solvents on Reaction Rates and DS

The impact of miscible co-solvents on reaction rates and the total degree of substitution (“DS”) were determined by comparing samples prepared according to the following methods. A 3-neck 100 mL round bottom flask was equipped with a double neck adapter giving four ports, an iC10 diamond tipped IR probe, for mechanical stirring, and a N₂/vacuum inlet. To the flask was added 50.15 g of 1-butyl-3-methylimidazolium propionate (“[BMIm]OPr”). While stirring rapidly, 4.07 g of cellulose (7.5 weight percent) was added to the [BMIm]OPr at room temperature. Vacuum was applied with the aid of a bleed valve. After reaching 0.6 mm Hg, a preheated 80° C. oil bath was raised to the flask. A clear solution was obtained 8 minutes after raising the oil bath. Stirring was continued for an additional 2.8 hours before the solution was allowed to cool to room temperature and stand under N₂ for 12 hours.

To the cellulose solution at room temperature was added a mixture containing 12.09 g of propionic anhydride (3.7 eq.) and 482 mg of MSA (0.2 eq.) dropwise over a period of 20 minutes. During the course of the reaction, aliquots were removed and the product was isolated by precipitation in 200 mL of methanol and filtering. The reaction was complete 20 minutes after the end of addition. The experiment was terminated and the remaining reaction mixture was processed in the same manner as the aliquots. The solid from each sample was washed 3 times with 200 mL portions of methanol then 1 time with 250 mL of methanol containing 8 weight percent of 35 weight percent H₂O₂. The white solids were then dried at a temperature of 60° C. and a pressure of 5 mm Hg. A second set of samples was prepared following the same procedure as outlined above, with the exception that the [BMIm]OPr contained 11.9 weight percent propionic acid as a miscible co-solvent.

FIG. 30 shows a plot of absorbance for a band at 1212 cm⁻¹ (propionate ester and propionic acid) versus contact time for each of the samples prepared as described above. The DS indicated in FIG. 30 correspond to the DS values for the samples obtained in each procedure. Relative to the reaction of cellulose dissolved in [BMIm]OPr (no propionic acid), the reaction rate of cellulose dissolved in [BMIm]OPr having 11.9 weight percent propionic acid is slower and the DS of each sample is higher than the corresponding sample from the other procedure. Thus, this example shows that, in addition to impacting solution viscosity, a co-solvent can also have a dramatic impact on reaction rates and the total DS obtained.

DEFINITIONS

As used herein, the terms “a,” “an,” “the,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

As used herein, the terms “containing,” “contains,” and “contain” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms, “including,” “include,” and “included” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

NUMERICAL RANGES

The present description uses numerical ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claims limitation that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds).

CLAIMS NOT LIMITED TO SINGLE EMBODIMENT

The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims. 

1. A process for making a cellulose ester, said process comprising: (a) adding a binary component to a halide ionic liquid; (b) dissolving cellulose in said halide ionic liquid; and (c) esterifying at least a portion of the dissolved cellulose in a reaction medium comprising said halide ionic liquid, said binary component, and an acylating reagent comprising a C₁ to C₂₀ alkyl carboxylic anhydride or carboxylic acid halide, an aryl carboxylic anhydride or carboxylic acid halide, or combination thereof, thereby producing said cellulose ester, wherein the degree of polymerization (DP) of the dissolved cellulose subjected to esterification in step (c) is within 10 percent of the DP of said cellulose dissolved in step (b).
 2. The process of claim 1, wherein said binary component is an acid or a functional ionic liquid.
 3. The process of claim 1, wherein said binary component is a Lewis acid.
 4. The process of claim 3, wherein said Lewis acid is characterized by the formula MX_(n), wherein M is a transition metal selected from the group consisting of B, Al, Fe, Ga, Sb, Sn, As, Zn, Mg, and Hg, wherein X is selected from the group consisting of halogen, carboxylate, sulfonate, alkoxide, alkyl, and aryl.
 5. The process of claim 1, wherein said binary component is a protic acid.
 6. The process of claim 5, wherein said protic acid is selected from the group consisting of methane sulfonic acid and p-toluene sulfonic acid.
 7. The process of claim 5, wherein said protic acid has a pK_(a) in the range of from about −5 to about
 10. 8. The process of claim 1, wherein said binary component is a functional ionic liquid.
 9. The process of claim 8, wherein said functional ionic liquid comprises the following structure:

wherein at least one of R₁, R₂, R₃, R₄, and R₅ is (CHX)_(n)Y, wherein X is hydrogen or a halide, wherein n is an integer in the range of from 1 to 10 inclusive, wherein Y is sulfonic or carboxylate, and wherein the remainder R₁, R₂, R₃, R₄, and R₅ groups each individually comprise hydrogen, a C₁ to C₁₀ alkyl group, a C₂ to C₁₀ alkenyl group, a C₁ to C₁₀ alkoxyalkyl group, or a C₁ to C₁₀ alkoxy group.
 10. The process of claim 8, wherein said functional ionic liquid comprises 1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluorobutyl)imidazolium, 1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium, 1-alkyl-3-(1-sulfonylethyl)imidazolium, 1-alkyl-3-(1-sulfonylpropyl)imidazolium, 1-alkyl-3-(1-sulfonylbutyl)imidazolium, and/or 1-alkyl-3-(1-sulfonylhexyl)imidazolium, wherein said alkyl comprises a C1 to C10 straight-chain alkyl group.
 11. The process of claim 1, wherein said cellulose comprises a plurality of anhydroglucose units (“AGU”), wherein said binary component is present in said reaction medium in an amount in the range of from about 0.01 to about 100 mol percent per AGU.
 12. The process of claim 1, wherein said halide ionic liquid comprises a plurality of cations and a plurality of anions, wherein at least a portion of the cations of said halide ionic liquid comprise imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations.
 13. The process of claim 1, wherein at least a portion of the anions of said halide ionic liquid are selected from the group consisting of chloride, bromide, iodide, fluoride, and mixtures of two of more thereof.
 14. The process of claim 1, wherein said reaction medium further comprises a carboxylic acid, wherein said carboxylic acid is present in said reaction medium in the range of from about 0.1 to about 25 weight percent by weight of the total reaction medium.
 15. The process of claim 14, wherein said carboxylic acid comprises acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, substituted benzoic acids, phthalic acid, and/or isophthalic acid.
 16. The process of claim 1, wherein said halide ionic liquid comprises 1-butyl-3-methylimidazolium chloride, wherein said reaction medium comprises said binary component in an amount in the range of from about 0.01 to about 100 mol percent per AGU, wherein said reaction medium has a viscosity of less than about 60,000 poise at 0.1 rad/sec at a temperature of 25° C.
 17. The process of claim 1, wherein said halide ionic liquid comprises 1-allyl-3-methylimidazolium chloride, wherein said reaction medium comprises said binary component in an amount in the range of from about 0.01 to about 100 mol percent per AGU, wherein said reaction medium has a viscosity of less than about 140,000 poise at 0.1 rad/sec at a temperature of 25° C.
 18. The process of claim 1, further comprising, prior to said esterifying, dissolving at least a portion of said cellulose in said halide ionic liquid to thereby form said reaction medium, wherein at least a portion of said acylating reagent is present during said dissolving of said cellulose.
 19. The process of claim 18, wherein during said dissolving, said acylating reagent is present in an amount in the range of from about 0.01 to about 20 molar equivalents based on the total amount of said cellulose in said reaction medium.
 20. The process of claim 1, wherein said cellulose ester comprises ester substituents, wherein at least 50 percent of said ester substituents comprise alkyl esters having a carbon chain length of at least 6 carbons, wherein said cellulose ester has a degree of substitution (“DS”) of at least 1.5.
 21. The process of claim 1, wherein said acylating reagent is present in an amount of less than 10 molar percent excess per AGU, wherein said cellulose ester has a DS of at least 2.0.
 22. A process for making cellulose esters, said process comprising: (a) dissolving a cellulose in a halide ionic liquid to thereby form an initial cellulose solution; (b) contacting said initial cellulose solution with a binary component and an acylating reagent comprising a C₁ to C₂₀ alkyl carboxylic anhydride or carboxylic acid halide, an aryl carboxylic anhydride or carboxylic acid halide, or combination thereof, under conditions sufficient to provide an acylated cellulose solution comprising a cellulose ester; (c) contacting said acylated cellulose solution with a non-solvent to cause at least a portion of said cellulose ester to precipitate and thereby provide a slurry comprising precipitated cellulose ester and at least a portion of said halide ionic liquid; (d) separating at least a portion of said precipitated cellulose ester from said halide ionic liquid to thereby provide a recovered cellulose ester and a separated halide ionic liquid; and (e) recycling at least a portion of said separated halide ionic liquid for use in dissolving additional cellulose, wherein the degree of polymerization (DP) of the dissolved cellulose subjected to acylation in step (b) is within 10 percent of the DP of said cellulose dissolved in step (a).
 23. The process of claim 22, wherein said binary component is an acid or a functional ionic liquid.
 24. The process of claim 22, wherein said binary component is a Lewis acid.
 25. The process of claim 24, wherein said Lewis acid is selected from the group consisting of ZnCl₂ and Zn(OAc)₂.
 26. The process of claim 22, wherein said binary component is a protic acid.
 27. The process of claim 26, wherein said protic acid is selected from the group consisting of methane sulfonic acid and p-toluene sulfonic acid.
 28. The process of claim 22, wherein said binary component is a functional ionic liquid.
 29. The process of claim 22, wherein said cellulose comprises a plurality of anhydroglucose units (“AGU”), wherein said binary component is present in said reaction medium in an amount in the range of from about 0.01 to about 100 mol percent per AGU.
 30. The process of claim 22, wherein said halide ionic liquid comprises a plurality of cations and a plurality of anions, wherein at least a portion of the cations of said halide ionic liquid comprise imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazolium cations, wherein at least a portion of the anions of said halide ionic liquid are selected from the group consisting of chloride, bromide, iodide, fluoride, and mixtures of two of more thereof.
 31. The process of claim 22, wherein at least a portion of said acylating reagent is present during said dissolving of step (a).
 32. The process of claim 22, wherein said acylating reagent is present in an amount of less than 20 molar percent excess per AGU, wherein said cellulose ester has a DS of at least 1.8.
 33. The process of claim 22, wherein said acylating reagent is present in an amount of less than 10 molar percent excess per AGU, wherein said cellulose ester has a DS of at least 2.0.
 34. The process of claim 22, wherein said cellulose ester is sufficiently soluble in acetone to produce an at least 10 weight percent cellulose ester solution in acetone, wherein said cellulose ester has a DS in the range of from 2.0 to 2.5.
 35. The process of claim 22, wherein at least 50 weight percent of said separated halide ionic liquid is recycled for use in dissolving additional cellulose.
 36. The process of claim 1, wherein said adding of step (a) is carried out after said dissolving of step (b). 